CVE-2026-55200
libssh2 - Out-of-Bounds Write via Unchecked packet_length in transport.c
- Published
- Jun 17, 2026
- Updated
- Jul 14, 2026
- Assigning CNA
- VulnCheck
- Evidence observed
- Aug 8, 2026
Primary CVSS
nvd · CVSS 4.0
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:XLow · next 30 days
- Percentile
- 90.2%
- Model date
- Sep 21, 2026
EPSS is a statistical estimate, not a certainty or a measure of impact. Combine it with CVSS, KEV status, exposure and your environment.
Summary
libssh2 through 1.11.1, fixed in commit 7acf3df 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.
Sources
4- CVE-2026-55200Informational
CVE-2026-55200
- CVE-2026-55200Informational
Detailed analysis of a critical pre-authentication out-of-bounds write vulnerability in libssh2 leading to remote code execution, with root cause, detection, and mitigation guidance.
Technical analysis and proof-of-concept for CVE-2026-55200, a critical heap-based buffer overflow in libssh2 allowing pre-authentication RCE. Includes mitigation guidance and supply-chain impact assessment.
Responsible use
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