libssh2: libssh2: Denial of Service via crafted SSH_MSG_EXT_INFO message

🗓️ 25 Jun 2026 13:02:46Reported by RedHatType

Libssh2 denial of service: rogue server can freeze clients during handshake by malformed extension information message, exhausting CPU.

Reporter	Title	Published	Views	Family All 66
GithubExploit	Exploitarium-Detections	28 Jun 202621:36	–	githubexploit
AlpineLinux	CVE-2026-55199	17 Jun 202618:44	–	alpinelinux
CBLMariner	CVE-2026-55199 affecting package libssh2 for versions less than 1.11.1-4	8 Jul 202616:02	–	cbl_mariner
Chainguard	CVE-2026-55199 vulnerabilities	14 Jul 202614:17	–	cgr
Circl	CVE-2026-55199	17 Jun 202622:46	–	circl
CVE	CVE-2026-55199	17 Jun 202618:44	–	cve
Cvelist	CVE-2026-55199 libssh2 - Pre-Authentication DoS via SSH_MSG_EXT_INFO Handler	17 Jun 202618:44	–	cvelist
Debian	[SECURITY] [DSA 6365-1] libssh2 security update	25 Jun 202618:20	–	debian
Debian CVE	CVE-2026-55199	17 Jun 202618:44	–	debiancve
Tenable Nessus	Debian dsa-6365 : libssh2-1-dev - security update	26 Jun 202600:00	–	nessus

OS	OS Version	Architecture	Package	Package Version	Filename
Red Hat Hardened Images	any	aarch64	libssh2	1.11.1-8.hum1	libssh2-1.11.1-8.hum1.aarch64.rpm
Red Hat Hardened Images	any	x86_64	libssh2	1.11.1-8.hum1	libssh2-1.11.1-8.hum1.x86_64.rpm
Red Hat Hardened Images	any	noarch	libssh2-docs	1.11.1-8.hum1	libssh2-docs-1.11.1-8.hum1.noarch.rpm

Source	Link
access	www.access.redhat.com/security/cve/CVE-2026-55199
bugzilla	www.bugzilla.redhat.com/show_bug.cgi
github	www.github.com/libssh2/libssh2/commit/17626857d20b3c9a1addfa45979dadcee1cd84a4
github	www.github.com/libssh2/libssh2/pull/1864
nvd	www.nvd.nist.gov/vuln/detail/CVE-2026-55199
cve	www.cve.org/CVERecord
vulncheck	www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler

19 Jul 2026 21:36Current

6.9Medium risk

Vulners AI Score6.9

CVSS 3.15.9 - 7.5

CVSS 48.2

EPSS0.00408

SSVC