CVE-2026-55199: libssh2 Infinite Loop
Vulnerability summary
CVE-2026-55199 is a high (CVSS 8.2) Infinite Loop vulnerability in libssh2. EPSS estimates a 0.92% chance of exploitation in the next 30 days, higher than 59.5% of scored vulnerabilities.
Advisory lineage
Upstream 0 · Downstream 8 · Related 8Timeline
- 17-06-2026PublishedVulnerability first disclosed.
- 14-07-2026Last modifiedVulnerability information updated.
Description
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
CVSS metrics
10 scores · 7 sources · 2 versions- OSV · UbuntuEcosystem advisory · calculated8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- OSV · WolfiEcosystem advisory · calculated8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- OSV · ChainguardEcosystem advisory · calculated8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
- NVDNIST8.2HighCVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
- OSV · AlpineEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HDiffers
- OSV · UbuntuEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HDiffers
- OSV · DebianEcosystem advisory · calculated7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HDiffers
- NVDNIST7.5HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:HDiffers
EPSS trend
Probability
0.92%
Chance of exploitation in the next 30 days
Percentile
60%
Versus all other CVEs
30-day change
0.00 pp
From 0.92% on 19-09-2026
Known exploited
Compare KEV catalogsNot in any of the 3 tracked catalogs.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeAffected systems
Suse15 products
- libssh2_org&distro=SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS< 1.11.0-150200.9.5.1 | < 1.11.0-150000.4.32.1
- libssh2_org&distro=SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS< 1.11.0-150200.9.5.1 | < 1.11.0-150000.4.32.1
- libssh2_org&distro=SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS< 1.11.0-150200.9.5.1
- libssh2_org&distro=SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS< 1.11.0-150200.9.5.1
- libssh2_org&distro=SUSE Linux Enterprise Micro 5.3< 1.11.0-150200.9.5.1
Chainguard3 products
- libssh2< 1.11.1-r7
- libssh2-dev< 1.11.1-r7
- libssh2-doc< 1.11.1-r7
Wolfi3 products
- libssh2< 1.11.1-r7
- libssh2-dev< 1.11.1-r7
- libssh2-doc< 1.11.1-r7
Alpine2 products
- libssh2< 1.11.1-r2 | < 1.11.1-r3
- rust< 1.96.1-r0
Debian1 product
- libssh2< 1.11.1-1+deb13u1 | < 1.11.1-4
Libssh21 product
- libssh2≤ 1.11.1
Ubuntu1 product
- libssh2< 1.11.0-4.1ubuntu0.24.04.2 | < 1.11.1-1ubuntu0.25.10.2 | < 1.11.1-1ubuntu0.26.04.2
7 vendors · 26 products
References
18 links- www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handlerThird Party AdvisoryAdvisory
Show all 18 references
- github.com/libssh2/libssh2PACKAGE