libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c
Priority HIGH 75CWE-680Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- None
- User interaction
- None
- Attack complexity
- Low
- Attack requirements
- Present
- Impact type
- —
- Confidentiality · integrity · availability
- High · High · High
- Fix status
- Partial Red Hat: 1 fixed, 2 without a fix
Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.
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.
Why it matters now
Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.03877 90th percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Partial Red Hat: 1 advisoryRed Hat: 1 fixed, 2 without a fix
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- Poc
- Automatable
- No
- Technical impact
- Total
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| The libssh2 Project | libssh2 | 1.11.1 | — | Patch available | CNA |
- libssh2 VendorThe libssh2 Project Affected 1.11.1 Fixed in — Patch available CNA
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:libssh2:libssh2:1.11.1:*:*:*:*:*:*:* | 1.11.1 | Vulnerable | The libssh2 Project |
- cpe:2.3:a:libssh2:libssh2:1.11.1:*:*:*:*:*:*:* Versions 1.11.1 Vulnerable ·The libssh2 Project
Remediation
Red Hat 1 advisory
- RHSA-2026:29950 Released 2026-06-25 · Red Hat rating ModerateRed Hat Hardened Images RPMs bug fix and enhancement update
- Red Hat Hardened Images libssh2-1.11.1-8.hum1@aarch64, libssh2-1.11.1-8.hum1@src, libssh2-1.11.1-8.hum1@x86_64 +4
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux 6 | Affected | No fix planned: Out of support scope |
| Red Hat Enterprise Linux 8 | Affected | No fix planned: Out of support scope |
| Red Hat Hardened Images | Fixed | RHSA-2026:29950 |
Not affected: 1 product
- Red Hat Enterprise Linux 7
Timeline
- 2026-10-02 Threatist record created from CVE-2026-55200
- 2026-10-03 Alias added: GHSA-r8mh-x5qv-7gg2
- 2026-10-16 EPSS moved to the 90th–95th percentile
- 2026-10-22 Fix available: libssh2/libssh2@97acf3dfda80c91c3a8c9f2372546301d4a1a7a8 · CNA
References
More The libssh2 Project Libssh2 vulnerabilities
- TI-2026-06681 libssh2 userauth.c userauth_password integer overflow CVSS 4.0MEDIUM 6.9
- TI-2023-26623 The SSH transport protocol with certain OpenSSH extensions, found in OpenSSH before 9.6… CVSS 3.1MEDIUM 5.9
- TI-2026-41806 libssh2 - Free of Uninitialized Pointer in publickey List Cleanup CVSS 4.0HIGH 8.3
- TI-2019-02869 Out-of-bounds read in libssh2 CVSS 3.1CRITICAL 9.1
- TI-2019-02865 Integer overflow in libssh2 CVSS 3.1HIGH 8.8
- TI-2019-02872 Out-of-bounds read in libssh2 CVSS 3.0CRITICAL 9.1
Sources
- CVE-2026-55200 · CVE Program
- CVE-2026-55200 · NVD
- FIRST EPSS
- GHSA-r8mh-x5qv-7gg2 · GitHub Advisory Database · CC BY 4.0
- CVE-2026-55200 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences