CVE catalog

CVE-2026-66035

Severity: High · CVSS 8.7
Published: Jul 24, 2026, 4:45:24 PM UTC
Source: [NVD] · [CVE record]
EPSS: 0.47% · Oct 25, 2026

libssh2 through 1.11.1, fixed in commit 42e33d8, contains a pre-authentication heap buffer overflow vulnerability that allows a malicious SSH server to corrupt heap metadata in any connecting client by sending a packet with a packet_length smaller than the cipher's block size during Encrypt-then-MAC cipher negotiation. In the fullpacket() function in src/transport.c, the ETM path allocates a buffer of packet_length bytes but copies blocksize minus one bytes via memcpy, causing an overflow that on 32-bit glibc writes attacker-controlled bytes into an adjacent chunk's SIZE field, enabling tcache bin confusion, overlapping live objects, and function pointer overwrite during the session handshake before authentication.

Vulnerable and fixed packages

Distribution-reported package versions and fixes. These do not depend on matching against the OpenFactory package catalog.

Distribution	Package	Release	Version	Status
Debian	libssh2	sid	`1.11.1-6`	fixed
Debian	libssh2	forky	`1.11.1-6`	fixed
Debian	libssh2	trixie	`1.11.1-1+deb13u2`	fixed
Debian	libssh2	trixie-security	`1.11.1-1+deb13u1`	vulnerable
Debian	libssh2	bookworm	`1.10.0-3`	not affected
Debian	libssh2	bookworm-security	`1.10.0-3+deb12u1`	not affected
Ubuntu	libssh2	noble	`1.11.0-4.1ubuntu0.24.04.4`	fixed
Ubuntu	libssh2-1-dev	noble	`1.11.0-4.1ubuntu0.24.04.4`	fixed
Ubuntu	libssh2-1t64	noble	`1.11.0-4.1ubuntu0.24.04.4`	fixed
Ubuntu	libssh2	pro	`1.8.0-2.1build1`	vulnerable
Ubuntu	libssh2	pro	`1.8.0-2.1ubuntu0.1`	vulnerable
Ubuntu	libssh2	pro	`1.8.0-2.1ubuntu0.1+esm1`	vulnerable
Ubuntu	libssh2	22.04	`1.9.0-3`	vulnerable
Ubuntu	libssh2	22.04	`1.10.0-2`	vulnerable
Ubuntu	libssh2	22.04	`1.10.0-2build1`	vulnerable
Ubuntu	libssh2	22.04	`1.10.0-3`	vulnerable
Ubuntu	libssh2	22.04	`1.10.0-3ubuntu0.1`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-2`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-3`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1build1`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1build2`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1ubuntu0.24.04.1`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1ubuntu0.24.04.2`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1ubuntu0.24.04.3`	vulnerable
Ubuntu	libssh2	24.04	`1.11.0-4.1ubuntu0.24.04.4`	fixed
Ubuntu	libssh2	26.04	`1.11.1-1build1`	vulnerable
Ubuntu	libssh2	26.04	`1.11.1-1build2`	vulnerable
Ubuntu	libssh2	26.04	`1.11.1-1ubuntu0.26.04.1`	vulnerable
Ubuntu	libssh2	26.04	`1.11.1-1ubuntu0.26.04.2`	vulnerable
Ubuntu	libssh2	26.04	`1.11.1-1ubuntu0.26.04.3`	vulnerable
Ubuntu	libssh2	26.04	`1.11.1-1ubuntu0.26.04.4`	fixed
Alpine	libssh2	3.21	`1.11.1-r3`	fixed
Alpine	libssh2	3.22	`1.11.1-r3`	fixed
Alpine	libssh2	3.23	`1.11.1-r4`	fixed
Alpine	libssh2	3.24	`1.11.1-r4`	fixed

Fixed-version evidence

Distribution	Package	Type	Release	Fixed version	Urgency	Origin	Bugs
Debian	libssh2	source	sid	`1.11.1-5`	not yet assigned	Not reported	[1142856]
Debian	libssh2	source	forky	`1.11.1-5`	not yet assigned	Not reported	[1142856]
Debian	libssh2	source	trixie	`1.11.1-1+deb13u2`	not yet assigned	Not reported	[1142856]
Debian	libssh2	source	bookworm	`Not affected`	unimportant	Not reported	[1142856]
Ubuntu	libssh2	deb	noble	`1.11.0-4.1ubuntu0.24.04.4`	Not reported	Not reported	Not reported
Ubuntu	libssh2-1-dev	deb	noble	`1.11.0-4.1ubuntu0.24.04.4`	Not reported	Not reported	Not reported
Ubuntu	libssh2-1t64	deb	noble	`1.11.0-4.1ubuntu0.24.04.4`	Not reported	Not reported	Not reported
Ubuntu	libssh2	deb	24.04	`1.11.0-4.1ubuntu0.24.04.4`	Not reported	UBUNTU-CVE-2026-66035	Not reported
Ubuntu	libssh2	deb	26.04	`1.11.1-1ubuntu0.26.04.4`	Not reported	UBUNTU-CVE-2026-66035	Not reported
Alpine	libssh2	apk	3.21	`1.11.1-r3`	Not reported	ALPINE-CVE-2026-66035	Not reported
Alpine	libssh2	apk	3.22	`1.11.1-r3`	Not reported	ALPINE-CVE-2026-66035	Not reported
Alpine	libssh2	apk	3.23	`1.11.1-r4`	Not reported	ALPINE-CVE-2026-66035	Not reported
Alpine	libssh2	apk	3.24	`1.11.1-r4`	Not reported	ALPINE-CVE-2026-66035	Not reported

[Debian bug #1142856]

OpenFactory catalog packages

[Debian 13 (Trixie)]

[libssh2-1-dev]Affected
Source package: [libssh2]
Details (4)
- 1.11.1-1+deb13u1 · amd64 · trixie
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · arm64 · trixie
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · amd64 · trixie-security
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · arm64 · trixie-security
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
[libssh2-1t64]Affected
Source package: [libssh2]
Details (4)
- 1.11.1-1+deb13u1 · amd64 · trixie
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · arm64 · trixie
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · amd64 · trixie-security
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13
- 1.11.1-1+deb13u1 · arm64 · trixie-security
  Affected · Fixed: 1.11.1-1+deb13u2
  nvd · libssh2 · debian · 13

[Debian 12 (Bookworm)]

[libssh2-1]Not affected
Source package: [libssh2]
Details (2)
- 1.10.0-3+b1 · amd64 · bookworm
  Not affected
  nvd · libssh2 · debian · bookworm
- 1.10.0-3+b1 · arm64 · bookworm
  Not affected
  nvd · libssh2 · debian · bookworm
[libssh2-1-dev]Not affected
Source package: [libssh2]
Details (2)
- 1.10.0-3+b1 · amd64 · bookworm
  Not affected
  nvd · libssh2 · debian · bookworm
- 1.10.0-3+b1 · arm64 · bookworm
  Not affected
  nvd · libssh2 · debian · bookworm

Observed: Oct 27, 2026, 7:11:53 AM UTC

References

[CERT-Bund public advisories] · [Debian Security Tracker] · [FIRST EPSS] · [National Vulnerability Database (NVD)] · [OSV Package Vulnerability Database] · [Red Hat security advisories and VEX] · [SUSE security advisories and VEX] · [Ubuntu Security Notices (USN)]