8.6

CVE-2026-5501: Improper Certificate Signature Verification in X.509 Chain Validation Allows Forged Leaf Certificates

Analyzed
AliasesUBUNTU-CVE-2026-5501DEBIAN-CVE-2026-5501ALPINE-CVE-2026-5501
Published 10-04-2026Last modified 22-04-2026

Vulnerability summary

CVE-2026-5501 is a high (CVSS 8.6) Improper Certificate Validation vulnerability in wolfssl. EPSS estimates a 0.32% chance of exploitation in the next 30 days, higher than 24.7% of scored vulnerabilities.

Priority
Routine

Not severe (CVSS 8.6, network access); no exploitation reported by the 5 checked sources

Source freshness unavailable

How is this decided?
CVSS score
8.6/10
010
High · v4.0 (CVE.org)
EPSS score
0.32%
0%100%
Low · +0.10 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits0No public exploits recorded

Timeline

  1. 10-04-2026
    PublishedVulnerability first disclosed.
  2. 22-04-2026
    Last modifiedVulnerability information updated.

Description

wolfSSL_X509_verify_cert in the OpenSSL compatibility layer accepts a certificate chain in which the leaf's signature is not checked, if the attacker supplies an untrusted intermediate with Basic Constraints `CA:FALSE` that is legitimately signed by a trusted root. An attacker who obtains any leaf certificate from a trusted CA (e.g. a free DV cert from Let's Encrypt) can forge a certificate for any subject name with any public key and arbitrary signature bytes, and the function returns `WOLFSSL_SUCCESS` / `X509_V_OK`. The native wolfSSL TLS handshake path (`ProcessPeerCerts`) is not susceptible and the issue is limited to applications using the OpenSSL compatibility API directly, which would include integrations of wolfSSL into nginx and haproxy.

CVSS metrics

7 scores · 5 sources · 2 versions

EPSS trend

Probability

0.32%

Chance of exploitation in the next 30 days

Percentile

25%

Versus all other CVEs

30-day change

Increase +0.10 pp

From 0.22% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

0 found

No public exploits indexed.

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.

Alpine1 product
  • wolfssl< 5.9.1-r0
Debian1 product
  • wolfsslAll versions (No fix recorded)
Ubuntu1 product
  • wolfsslAll versions (No fix recorded)
Wolfssl1 product

4 vendors · 4 products

References

5 links