libssh2 through 1.11.1, fixed in commit 7acf3df contains... · CVE-2026-55200 · GitHub Advisory Database · GitHub
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libssh2 through 1.11.1, fixed in commit 7acf3df contains...
Critical severity
Unreviewed
Published<br>Jun 17, 2026<br>to the GitHub Advisory Database
•<br>Updated Jun 30, 2026
Package
No package listed—<br>Suggest a package
Affected versions
Unknown
Patched versions
Unknown
Description
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.
References
https://nvd.nist.gov/vuln/detail/CVE-2026-55200
libssh2/libssh2#2052
libssh2/libssh2@97acf3d
https://www.vulncheck.com/advisories/libssh2-out-of-bounds-write-via-unchecked-packet-length-in-transport-c
https://github.com/bikini/exploitarium/tree/main/libssh2-cve-2026-55200-poc
https://web.archive.org/web/20260623211210/https://github.com/bikini/exploitarium/tree/main/libssh2-cve-2026-55200-poc
Published by the National Vulnerability Database<br>Jun 17, 2026
Published to the GitHub Advisory Database<br>Jun 17, 2026
Last updated<br>Jun 30, 2026
Severity
Critical
9.2
CVSS overall score
This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10
CVSS v4 base metrics
Exploitability Metrics
Attack Vector<br>Network
Attack Complexity<br>Low
Attack Requirements<br>Present
Privileges Required<br>None
User interaction<br>None
Vulnerable System Impact Metrics
Confidentiality<br>High
Integrity<br>High
Availability<br>High
Subsequent System Impact Metrics
Confidentiality<br>None
Integrity<br>None
Availability<br>None
Learn more about base metrics
CVSS v4 base metrics
Exploitability Metrics
Attack Vector:<br>This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity:<br>This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements:<br>This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required:<br>This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction:<br>This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the...