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Public proof of concept

CVE-2026-55200

A public proof of concept exists; no exploitation attested.

  • Published2026-06-17
  • WeaknessCWE-680

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

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.

Timeline

dates in UTC
  1. 2026-06-1720:17CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 15:37 UTC
Indicators tagged with this CVE, per day0 indicators over 7 days
Block these indicators
  • Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2026-55200?format=txt
  • CSV export: https://api.ismalicious.com/edl/cve/CVE-2026-55200?format=csv
  • TAXII collection of exploited CVEs
  • The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD
Libssh2
BranchAffectedFixed in
1.11= 1.11.1no fix published

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Distribution builds and vendor advisories

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Vendor advisories

  • CVE-2026-55200 Red Hat Product Security7 products fixed · 8 known affected

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

    libssh2 as a component of Red Hat Enterprise Linux 6 · libssh2-devel as a component of Red Hat Enterprise Linux 6 · libssh2-docs as a component of Red Hat Enterprise Linux 6 · +5 more

  • RHSA-2026:29950 Red Hat Product Security7 products fixed

    Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update

Full record on NVD

Fix

  1. Vendor fix Red Hat Product Security RHSA-2026:29950 · 7 productsFor details on how to apply this update, which includes the changes described in this advisory, refer to: https://images.redhat.com/
  2. Workaround from the vendor Red Hat Product Security RHSA-2026:29950 · 7 productsThe primary mitigation is strict network access control. Ensure libssh2 clients only connect to trusted SSH servers, and use firewalls to block untrusted incoming connections if libssh2 is deployed as a server-side application.
  3. No fix planned, says the vendor Red Hat Product Security CVE-2026-55200 · 8 productsOut of support scope

Advisories and patches

Detection

Nuclei template
none so far
ProjectDiscovery
Exploit-DB
no entry
Exploit-DB
Proof-of-concept repositories
3 repositories, unverified0xBlackash/CVE-2026-55200xd20111/CVE-2026-55200kaleth4/CVE-2026-55200
PoC-in-GitHub

Sources

Technical details

CVSS v3 Vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L
CVSS 4.0 vector
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
Published
2026-06-17
Last Modified
2026-10-22
NVD status
Modified
MSRC Title
libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c

Frequently asked questions

What is CVE-2026-55200?

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.

Is CVE-2026-55200 actively exploited?

A proof-of-concept exploit exists for CVE-2026-55200, but active exploitation has not been confirmed at this time.

What is the CVSS score for CVE-2026-55200?

CVE-2026-55200 has a CVSS v3 base score of 8.3 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:L.

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