CveMateVulnerability intelligence

Erlang OTP vulnerabilities, page 2

64 vulnerabilities

Known vulnerabilities in Erlang OTP, newest first, with CVSS severity, EPSS, KEV listings, ransomware use and the affected versions.

CVE-2026-73812debianerlang+21mo ago01-09-2026 14:42

httpd function check_header/3 rejects duplicate Content-Length (per CVE-2026-23941) but never checks for the TE+CL co-presence that RFC 9112 §6.3 identifies as a probable smuggling attempt. handle_body/3 frames by chunked and silently discards Content-Length. A CL-preferring front-end paired with chunked-preferring inets creates a classic CL.TE front-end/back-end desync. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.CVE-2026-73276debianerlang+21mo ago01-09-2026 14:41

Gracefulness code ignored cases that should be rejected, resulting in possible HTTP Request Smuggling opportunities. This issue affects OTP from OTP 22.2 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 7.1.2 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2.CVE-2026-73270debianerlang+21mo ago01-09-2026 14:48

Improper Handling of Case Sensitivity vulnerability in Erlang/OTP inets httpd allows a remote unauthenticated attacker to read files inside a mod_auth protected directory by requesting them with different casing, on deployments whose filesystem is case-insensitive. mod_auth:secret_path/3 decides whether a resolved filesystem path lies inside a protected directory block by running the configured directory path through re:run/3 without the caseless option. A request for /secret/file against a directory configured as /Secret therefore does not match, so the request is treated as unprotected and no authentication challenge is issued, while the filesystem resolves the differently cased path to the same file and mod_get serves it. Deployments on case-sensitive filesystems are unaffected, because there the filesystem itself rejects the mismatched casing. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.CVE-2026-71380debianerlang+21mo ago01-09-2026 14:35

Missing Release of Resource after Effective Lifetime vulnerability in Erlang/OTP inets httpd allows an unauthenticated remote attacker to cause denial of service by sending valid request headers with a large Content-Length and then stalling before the body is complete. httpd_request_handler:handle_info/2 cancels the request timeout as soon as a parse step succeeds, which includes the headers, and the clause that handles a decoder asking for more data re-arms the socket with {active, once} without setting any further timer. httpd_request:whole_body/2 returns such a continuation whenever the bytes received are fewer than the announced Content-Length, so a well-formed request that stops mid-body leaves the worker waiting indefinitely. The periodic byte-rate check that would reclaim it is armed only when minimum_bytes_per_second is configured, which it is not by default. Repeating this across connections occupies every worker permitted by max_clients and denies service to legitimate clients at negligible bandwidth cost. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.CVE-2026-71562erlangotp1mo ago01-09-2026 14:33

Improper Validation of Specified Quantity in Input vulnerability in Erlang/OTP inets httpc allows a malicious or compromised HTTP server to degrade availability by returning a numeric header whose value is a very long run of digits. httpc_handler.erl converts the server-supplied Content-Length with list_to_integer/1 before comparing it against max_body_size, so the size check cannot protect the conversion, and the option defaults to nolimit in any case. The same unbounded conversion appears in httpc_response:format_response/1 for Content-Length and in httpc_response:get_ms_from_retry_after/1 for Retry-After, which is guarded only by a check that the first character is a digit. A value of up to roughly 1.26 million digits converts successfully and costs the requesting process hundreds of milliseconds of arbitrary-precision arithmetic per response. The conversion function is documented to accept integers of any size, so bounding the input is the caller's responsibility. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.CVE-2026-59250debianerlang+22mo ago27-07-2026 15:25

Classic buffer overflow in the Erlang/OTP megaco flex scanner C driver allows a remote unauthenticated attacker to corrupt the driver's memory (and potentially achieve remote code execution or a denial-of-service crash) by sending a single text-encoded H.248/Megaco message containing an oversized property parm name. When tokenizing a Local/Remote descriptor, mfs_load_property_groups extracts the attacker-controlled property name (bounded only by the message length) and, when no value follows, formats it into a fixed 512-byte error_msg field of the MfsErlDrvData struct using an unchecked sprintf call. Names longer than roughly 452 bytes overflow into the immediately following struct fields (text_buf, text_ptr, term_spec, term_spec_size, term_spec_index), overwriting live pointers and counters with attacker-chosen bytes. Subsequent scanner code writes and frees through the corrupted pointers, producing arbitrary write and arbitrary free primitives inside the BEAM VM process, which can be leveraged for remote code execution. On builds compiled with _FORTIFY_SOURCE the overflow is detected at runtime and terminates the process with SIGABRT, resulting in denial of service. The overflow occurs in the flex scanner before any grammar or Megaco-level authentication processing, so exploitation requires only network reachability to the megaco transport port on a node configured with {scanner, flex}. This vulnerability is associated with program files lib/megaco/src/flex/megaco_flex_scanner_drv.flex.src and program routines mfs_load_property_groups. This issue affects OTP from OTP 17.0 before OTP 27.3.4.15, from OTP 28.0 before OTP 28.5.0.4, and from OTP 29.0 before OTP 29.0.4, corresponding to megaco from 3.17.1 before 4.7.2.2, from 4.8 before 4.8.3.1, and from 4.9 before 4.9.1. Whether OTP before OTP 17.0, corresponding to megaco before 3.17.1, is affected is unknown.CVE-2026-59696debianerlang+21mo ago01-09-2026 14:37

Improper Validation of Specified Quantity in Input vulnerability in Erlang/OTP stdlib allows a remote attacker to degrade availability by supplying a URI whose port component is a very long run of digits. uri_string:get_port/1 passes the port substring to binary_to_integer/1 with no length bound, catching only error:badarg, so a syntactically valid port of up to roughly 1.26 million digits converts successfully and costs the calling process hundreds of milliseconds of arbitrary-precision arithmetic. The conversion is reached from every authority-parsing path in uri_string:parse/1, including the host, registered-name, and IPv4 and IPv6 forms. parse/1 is the documented interface for parsing URIs, so any application that parses an attacker-supplied URI is exposed without further configuration. The conversion function is documented to accept integers of any size, so bounding the input is the caller's responsibility. This issue affects OTP from OTP 21.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to stdlib from 3.5 before 6.2.2.5, from 7.0 before 7.3.0.2, and from 8.0 before 8.0.4.CVE-2026-59251debianerlang+42mo ago27-07-2026 15:30

Allocation of resources without limits in Erlang/OTP public_key certificate path validation allows a remote unauthenticated attacker to cause denial of service by sending a crafted X.509 certificate chain during the TLS handshake. During RFC 5280 policy processing in public_key:pkix_path_validation/3, the certificate policy tree maintained by pubkey_policy_tree grows without an upper bound. When a certificate chain contains M policies per certificate and K certificates, the tree grows on the order of M^K nodes because pubkey_policy_tree:add_leaves/2 and pubkey_policy_tree:add_leaf_siblings/2 extend the tree per policy per certificate. A modest chain with many policies per certificate is enough to pin BEAM schedulers and exhaust the node's memory, taking down the entire VM. The attacker only needs to be able to present a certificate chain to the victim, which is the normal precondition for a TLS handshake, so exploitation succeeds against any incoming or outgoing TLS connection that validates the peer's chain (the default for SSL/TLS clients and mutual-TLS servers). This is the same vulnerability class as OpenSSL's X509_verify_cert policy tree DoS. This vulnerability is associated with program files lib/public_key/src/pubkey_policy_tree.erl and program routines pubkey_policy_tree:add_leaves/2 and pubkey_policy_tree:add_leaf_siblings/2. This issue affects OTP from OTP 26.2 before OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to public_key from 1.15 before 1.21.4, 1.20.3.4 and 1.17.1.5.CVE-2026-55951debianerlang+21mo ago01-09-2026 14:37

The Erlang/OTP httpc HTTP client does not enforce a limit on the total size of response headers received from a server. The max_header_size option defaults to nolimit, and httpc_response:parse_headers/6 accumulates every header into a list before the length check runs (which only fires after the terminating CRLF CRLF is received). A malicious or compromised HTTP server can send an arbitrarily large number of headers, or headers with very large values, causing the client process to allocate unbounded memory until the system runs out of memory or the BEAM VM crashes. A proof-of-concept server sending 100,000 headers of roughly 4000 bytes each caused the client VM to allocate over 13 GB of memory in under 30 seconds. Any application using httpc:request/4,5 to connect to untrusted servers is affected. No authentication is required: any server the client connects to (including via a redirect or man-in-the-middle) can trigger the exhaustion. This issue affects OTP from OTP 17.0 before OTP 27.3.4.17, from OTP 28.0 before OTP 28.5.0.6, and from OTP 29.0 before OTP 29.0.6, corresponding to inets from 5.10 before 9.3.2.7, from 9.4 before 9.6.2.3, and from 9.7 before 9.7.2. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.CVE-2026-55953debianerlang+42mo ago27-07-2026 15:21

The Erlang/OTP ssl TLS 1.2 (and earlier) and DTLS client does not verify that the cipher suite selected by the server in ServerHello was among the suites offered by the client in ClientHello. The client-side tls_handshake:hello/5 handler validates the negotiated protocol version and the downgrade sentinel but hands the server-chosen suite directly to ssl_handshake:handle_server_hello_extensions/9, which installs it without a membership check. The TLS 1.3 client path performs this check (per RFC 8446), so it is not affected. An on-path attacker between the client and the intended server can respond with a ServerHello selecting an anonymous key exchange suite such as TLS_DH_anon_* or TLS_ECDH_anon_* that the client never offered. Anonymous suites do not require the server to present a certificate, so the entire verify_peer and cacerts configuration is bypassed: the attacker completes the handshake with its own ephemeral parameters, no certificate is validated, no hostname is checked, and ssl:connect returns {ok, Socket}. All subsequent application traffic is readable and modifiable by the attacker. This issue affects OTP from OTP 17.0 before OTP 27.3.4.15, from OTP 28.0 before OTP 28.5.0.4, and from OTP 29.0 before OTP 29.0.4, corresponding to ssl from 5.3.4 before 11.2.12.11, from 11.3 before 11.6.0.4, and from 11.7 before 11.7.4. Whether OTP before OTP 17.0, corresponding to ssl before 5.3.4, is affected is unknown.CVE-2026-55737debianerlang+42mo ago27-07-2026 15:13

Signed to Unsigned Conversion Error and Out-of-bounds Write vulnerability in Erlang OTP erts allows an attacker who can supply a crafted Erlang external term format (ETF) binary to binary_to_term/1 to corrupt the BEAM heap pointer and crash the virtual machine. When decoding a LARGE_TUPLE_EXT term, the validation pass decoded_size() in erts/emulator/beam/external.c reads the 32-bit arity field as unsigned (get_uint32()), while the decode pass dec_term() reads the same field as a signed 32-bit integer (get_int32()) into an int. An arity wire value of 0x80000000 passes validation as 2147483648 but decodes as -2147483648, so the subsequent hp += n moves the heap allocation pointer backward. Neither pass enforces the runtime tuple-arity limit MAX_ARITYVAL. The result is an out-of-bounds heap write; in practice the VM detects an impossible heap size and aborts, denying service. The required padding is large when uncompressed but the compressed-ETF envelope shrinks it to a small payload on the wire. This issue affects OTP from OTP 25.0 before OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15, corresponding to erts from 13.0 before 17.0.4, 16.4.0.4 and 15.2.7.11.CVE-2026-55950debianerlang+43mo ago02-07-2026 16:06

Time-of-check Time-of-use (TOCTOU) race condition vulnerability in Erlang/OTP ssl (dtls_packet_demux module) allows an unauthenticated remote attacker to crash all active DTLS sessions on a listener. A DTLS server listener uses a single shared dtls_packet_demux gen_server process to route incoming UDP datagrams to the correct connection handler. When a DTLS client reconnects rapidly from the same source address and port (sending multiple ClientHello messages in quick succession), a race condition in the demux's internal gb_trees key-value store causes a {key_exists, {old, Client}} crash, terminating the demux process. Because the demux is shared across all DTLS associations on that listener, its crash immediately kills every active DTLS session, not just the attacker's. The attack is pre-authentication: the attacker only needs to send UDP datagrams containing valid ClientHello messages from the same source IP and port before the intermediate DOWN monitor message is processed by the gen_server. No credentials, no completed handshake, and no special configuration are required, and the crash can be repeated indefinitely to create a persistent denial of service for all clients of that listener. This vulnerability is associated with program file lib/ssl/src/dtls_packet_demux.erl. This issue affects OTP from OTP 25.3 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 10.9 before 11.7.3, 11.6.0.3 and 11.2.12.10.CVE-2026-55952debianerlang+43mo ago02-07-2026 16:06

The Erlang/OTP ssl application does not validate that the PSK identity list and binder list carried in a TLS 1.3 ClientHello pre-shared key extension have equal length before passing them to the session ticket handler. In tls_handshake_1_3:handle_pre_shared_key/3, an OfferedPreSharedKeys record with a mismatched number of identities and binders is forwarded directly to tls_server_session_ticket:use/4, which crashes the session ticket handler process. An unauthenticated remote attacker can send a single crafted ClientHello to a TLS 1.3 server with session tickets enabled (stateful or stateless mode) and permanently disrupt session ticket handling on that listener. New TLS 1.3 handshakes complete but subsequently crash when the server attempts to issue a session ticket, effectively making TLS 1.3 unusable on the affected listener until the ssl application is restarted. TLS 1.2 connections are not affected. This issue affects OTP from OTP 22.2 before OTP 29.0.3, OTP 28.5.0.3 and OTP 27.3.4.14, corresponding to ssl from 9.5 before 11.7.3, 11.6.0.3 and 11.2.12.10.CVE-2026-65634debianerlang+226d ago22-09-2026 08:49

Inefficient algorithmic complexity in the Erlang/OTP asn1 OBJECT IDENTIFIER decoder allows a remote unauthenticated attacker to cause denial of service by sending a crafted OID during the TLS handshake. The BER OID decoder asn1rtt_ber:dec_subidentifiers/3 in lib/asn1/src/asn1rtt_ber.erl and the equivalent PER helper asn1rtt_per_common:dec_subidentifiers/3 in lib/asn1/src/asn1rtt_per_common.erl accumulate a base-128 subidentifier into an unbounded integer using (Av bsl 7) + H per continuation byte. Each shift and addition on the growing accumulator is linear in the number of bits already accumulated, giving quadratic total work in the size of a single subidentifier. The JER helper asn1rtt_jer:json2oid/1 in lib/asn1/src/asn1rtt_jer.erl exhibits the same class of unbounded-integer parsing when decoding a dot-separated OID from JSON. A DER-encoded OBJECT IDENTIFIER with one very large arc (approximately 262 KB of continuation bytes) consumes roughly 13 seconds of CPU on typical hardware. The vulnerable decoder is generated into every ASN.1 module that contains an OBJECT IDENTIFIER, including OTP-PUB-KEY which is reached during X.509 certificate parsing via public_key:pkix_decode_cert/2. This decoder runs before any signature or trust chain verification, so any Erlang service that parses peer TLS certificates is exposed: the default for TLS clients (which always parse the server certificate) and for mutual-TLS servers (which parse client certificates). This vulnerability is associated with program files lib/asn1/src/asn1rtt_ber.erl, lib/asn1/src/asn1rtt_per_common.erl and lib/asn1/src/asn1rtt_jer.erl and program routines asn1rtt_ber:dec_subidentifiers/3, asn1rtt_per_common:dec_subidentifiers/3 and asn1rtt_jer:json2oid/1. This issue affects OTP from OTP 17.0 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to asn1 from 3.0 before 5.3.4.3, 5.4.3.1, and 5.5.2. Whether OTP before OTP 17.0, corresponding to asn1 before 3.0, is affected is unknown.CVE-2026-68956debianerlang+226d ago22-09-2026 08:49

Allocation of Resources Without Limits or Throttling vulnerability in Erlang/OTP ssh allows an authenticated remote attacker to exhaust node memory by repeatedly opening session channels that are never assigned a handler. The "session" clause of ssh_connection:handle_msg/4 checks only minimal_remote_max_packet_size before calling setup_session/5, which unconditionally builds a #channel{} record and stores it in the ETS channel cache. The max_channels daemon option is consulted only by ssh_channel_sup:max_num_channels_not_exceeded/2, which counts supervisor children, so a channel that never gets a shell, exec, or subsystem handler is invisible to the limit and setting the option to a finite value does not mitigate the attack. RFC 4254 section 5.1 permits many session channels per connection, and each record costs only a few hundred bytes, so a single authenticated connection can accumulate channels until the node runs out of memory and the emulator terminates, affecting every application on it. No file contents, credentials, or write access are obtainable. This issue affects OTP from OTP 18.1.2 before OTP 27.3.4.18, OTP 28.5.0.7, and OTP 29.1.1, corresponding to ssh from 4.1.1 before 5.2.11.13, 5.5.2.6, and 6.0.6. Whether OTP before OTP 18.1.2, corresponding to ssh before 4.1.1, is affected is unknown.CVE-2026-47078debianerlang+22mo ago27-07-2026 15:03

Relative Path Traversal vulnerability in Erlang OTP (stdlib zip module) allows writing files outside the intended extraction directory via a crafted zip archive. zip:unzip/1,2 and zip:extract/1,2 validate entry paths using zip:check_dir_level/2, which tracks directory depth as a running integer counter: .. decrements it, normal path components increment it. The caller rejects only paths where the final counter value is less than zero. A path such as ../x/y causes the counter to go negative mid-traversal then recover to zero, passing validation while resolving to a location outside the extraction directory when joined with the current working directory via add_cwd. This vulnerability is associated with program file lib/stdlib/src/zip.erl. This issue affects OTP from OTP 27.1 before OTP 27.3.4.15, OTP 28.5.0.4, and OTP 29.0.4, corresponding to stdlib from 6.1 before 6.2.2.4, 7.3.0.1, and 8.0.3.CVE-2026-42792debianerlang+42mo ago27-07-2026 14:58

Improper Handling of Exceptional Conditions vulnerability in Erlang OTP erts (epmd) allows an unauthenticated remote attacker to permanently terminate the Erlang Port Mapper Daemon (epmd) via connection slot exhaustion. The do_accept function in erts/epmd/src/epmd_srv.c calls epmd_cleanup_exit() when accept(2) returns EMFILE (per-process file descriptor limit reached) or ENFILE (system-wide file descriptor limit reached), rather than treating these as recoverable conditions. An attacker can exhaust epmd's file descriptor slots by holding many TCP connections open while periodically sending a single byte to reset the idle timeout, then causing accept(2) to return EMFILE, which kills the daemon. epmd has no per-source-IP connection cap, making the attack feasible from a single source. On Debian/Ubuntu default packaging the impact is amplified: the systemd unit inherits a low file descriptor soft limit, and repeated daemon deaths trigger systemd's start-rate-limit, permanently failing both epmd.service and epmd.socket and requiring manual operator intervention to recover. This issue affects OTP from OTP 17.0 before OTP 29.0.4, OTP 28.5.0.4 and OTP 27.3.4.15.CVE-2026-42790debianerlang+34mo ago27-05-2026 15:09

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_cert and public_key modules) allows a DNS nameConstraints bypass via subject CommonName fallback in TLS hostname verification. Two flaws combine to allow a subordinate CA whose DNS nameConstraints are restricted (e.g. permitted;DNS:allowed.example.com) to issue a leaf certificate that an OTP TLS client accepts as a valid identity for an out-of-scope hostname (e.g. victim.example.com): First, pubkey_cert:validate_names/6 in lib/public_key/src/pubkey_cert.erl only checks SAN DNS entries against nameConstraints. Per RFC 5280, a permitted DNS subtree only restricts certificates that contain a DNS-typed name. A leaf with no subjectAltName therefore trivially satisfies any permitted;DNS:... constraint regardless of its subject commonName. Second, public_key:pkix_verify_hostname/3 in lib/public_key/src/public_key.erl falls back to the subject commonName when no subjectAltName is present, extracting id-at-commonName attributes as presented IDs and matching them against the reference hostname. The strict pkix_verify_hostname_match_fun(https) matcher does not suppress this fallback. The result is that path validation accepts a CN-only leaf under a DNS-constrained intermediate (no SAN means the nameConstraints are not triggered), and hostname verification then accepts it via the CN fallback. The bypass is reachable from stock ssl:connect with verify_peer, a trusted CA, SNI, and the canonical strict https hostname matcher. This issue affects OTP from OTP 19.3 before OTP 29.0.1, OTP 28.5.0.1, OTP 27.3.4.12 and OTP 26.2.5.21, corresponding to public_key from 1.4 before 1.21.1, 1.20.3.1, 1.17.1.3 and 1.15.1.7.CVE-2026-42791debianerlang+34mo ago27-05-2026 12:23

Improper Certificate Validation vulnerability in Erlang OTP public_key (pubkey_ocsp module) allows forged OCSP responses signed with an expired responder certificate to be accepted as valid. OCSP response verification in pubkey_ocsp:verify_response/5 and pubkey_ocsp:is_authorized_responder/3 in lib/public_key/src/pubkey_ocsp.erl does not check the validity period (notBefore/notAfter) of the OCSP responder certificate. An attacker who has obtained the private key of an expired CA-designated OCSP responder certificate can forge OCSP responses that Erlang/OTP accepts as valid. This affects TLS clients using OCSP stapling via the ssl application: a malicious or compromised server can present a revoked TLS certificate together with a forged OCSP response signed by an expired responder key, and the client will accept the revoked certificate as valid. It also affects applications calling public_key:pkix_ocsp_validate/5 directly, where the impact depends on the use case — server-side client certificate validation using this API may allow authentication bypass with a revoked client certificate. This issue affects OTP from OTP 27.0 before OTP 29.0.1, OTP 28.5.0.1 and OTP 27.3.4.12, corresponding to public_key from 1.16 before 1.21.1, 1.20.3.1 and 1.17.1.3.CVE-2026-42789debianerlang+34mo ago27-05-2026 12:23

Improper Following of a Certificate's Chain of Trust vulnerability in Erlang OTP public_key (pubkey_cert module) allows a non-CA certificate to be accepted as an intermediate issuer, enabling certificate chain forgery. In lib/public_key/src/pubkey_cert.erl, pubkey_cert:validate_extensions/7 contains two flaws that together allow a certificate with basicConstraints cA:false and no keyUsage extension to be used as an intermediate issuer in a chain passed to public_key:pkix_path_validation/3: the cA:false clause recurses into the remaining extensions without rejecting the certificate when it is in issuer position, and the keyUsage check only fires when the extension is present, so a certificate lacking keyUsage entirely bypasses the keyCertSign enforcement. Any party holding an end-entity certificate with basicConstraints cA:false and no keyUsage extension, issued by any CA in the victim's trust store, can use that certificate's private key to sign forged leaf certificates for arbitrary identities. public_key:pkix_path_validation/3 accepts the resulting chain, and by extension every TLS or mTLS endpoint built on the OTP ssl application that relies on the default verifier is affected, including server identity verification on the client side and client certificate verification on mTLS servers. This issue affects OTP from OTP 17.0 before OTP 27.3.4.19, OTP 28.5.0.8, and OTP 29.1.2, corresponding to public_key from 0.22 before 1.17.1.7, 1.20.3.6, and 1.21.8. Whether OTP before OTP 17.0, corresponding to public_key before 0.22, is affected is unknown.