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Fencer Vulns
high 8.1

CVE-2026-55200 json

libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c

published 2026-06-17 4 mo ago modified 2026-11-08 24 h ago also EUVD-2026-37784 , GHSA-r8mh-x5qv-7gg2 , JLSEC-2026-661

cvss
8.1
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
3.9%
EPSS 3.9% chance of exploitation in 30 days, percentile 90%
public exploits
0
none known

Summary

libssh2 1.11.1, fixed in commit 97acf3d, contains an out-of-bounds write vulnerability in ssh2_transport_read() that fails to enforce upper bounds on packet_length field. Remote attackers can send crafted SSH packets with excessively large packet_length values to corrupt heap memory and achieve remote code execution.

Patch / fix

  • julia LibSSH2_jll 1.11.102+0
  • libssh2 Debian 13 1.11.1-1+deb13u1
  • libssh2 Debian 14 1.11.1-4

debian advisories DEBIAN-CVE-2026-55200

  • libssh2 Ubuntu 25.10 1.11.1-1ubuntu0.25.10.2
  • libssh2 Ubuntu 26.04 LTS 1.11.1-1ubuntu0.26.04.2

ubuntu advisories UBUNTU-CVE-2026-55200

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libssh2 hummingbird 1 1.11.1-8.hum1

red hat advisories RHSA-2026:29950

  • libssh2_org SLES 16.0, Linux Micro 6.2, SLES for SAP applications 16.0 1.11.1-160000.4.1

suse advisories SUSE-SU-2026:22284-1SUSE-SU-2026:22364-1

  • libssh2_org openSUSE Leap 16.0 1.11.1-160000.4.1
  • libssh2_org openSUSE Tumbleweed 1.11.1-3.1

opensuse advisories openSUSE-SU-2026:21057-1openSUSE-SU-2026:11109-1

  • rust Alpine 3.24 1.96.1-r0
  • libssh2 Alpine 3.22, Alpine 3.21 1.11.1-r2
  • libssh2 Alpine 3.24, Alpine 3.23 1.11.1-r3
  • chromium-rust Alpine 3.24 1.96.1-r0

alpine advisories ALPINE-CVE-2026-55200

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libssh2 Azure Linux 3.0 1.11.1-3

azure linux advisories AZL-90927

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-55200 updated cvss 7.1

libssh2: libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c

  • Red Hat Enterprise Linux 6 libssh2 Red Hat Enterprise Linux 8 libssh2
    affected: workaround, no fix planned “Out of support scope”
  • Red Hat Hardened Images libssh2 1.11.1-8.hum1
    fixed: vendor fix RHSA-2026:29950
  • Red Hat Enterprise Linux 7 libssh2
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
Proof of concept is public
Automatable
no
Technical impact
total
Assessed
4 mo ago

Exploit prediction

3.88% chance of exploitation in the next 30 days, higher than 90% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • web.archive.org https://web.archive.org/web/20260623211210/https://github.com/bikini/exploitarium/tree/main/libssh2-cve-2026-55200-poc referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
CNA 3.1 8.1 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
CNA 4.0 9.2 CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/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
NVD 3.1 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
OSV 3.1 8.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L

Affected packages

ecosystem package affected fixed in
julia LibSSH2_jll
<1.11.102+0
1.11.102+0

Affected products

  • libssh2 libssh2

Classification

Weakness
  • CWE-680 Integer Overflow to Buffer Overflow

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.