Description
libssh2 through 1.11.1, fixed in commit a2ed82d, contains a pre-authentication integer underflow vulnerability in the ssh2_cipher_crypt() function in src/openssl.c that allows a malicious SSH server to crash any connecting client by negotiating AES-GCM ciphers during handshake. Attackers can exploit the underflow in the expression computing blocksize minus aadlen minus authentication tag length to trigger an out-of-bounds read and a memcpy call with a near-SIZE_MAX length argument, causing immediate process crash before any authentication occurs.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| libssh2 | libssh2 | ≤ 1.11.1 | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | libssh2 | 1.11.1-5 | — |
| Debian 13 | libssh2 | 1.11.1-1+deb13u2 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | libssh2 | 1.11.1-1ubuntu0.26.04.4 | USN-8722-1 |
| Ubuntu 24.04 LTS | libssh2 | 1.11.0-4.1ubuntu0.24.04.4 | USN-8722-1 |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | libssh2 +2 | 1.11.1-10.2.hum1 | RHSA-2026:46927 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | libssh2_org | 1.11.0-150600.20.6.1 | SUSE-SU-2026:3541-1 |
| SLES 15 SP6 | libssh2_org | 1.11.0-150600.20.6.1 | SUSE-SU-2026:3541-1 |
| SLES 15 SP5 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLES 15 SP4 | libssh2_org | 1.11.0-150000.4.35.1 | SUSE-SU-2026:4095-1, SUSE-SU-2026:3526-1 |
| SLES 12 SP5 | libssh2_org | 1.11.0-29.18.1 | SUSE-SU-2026:3525-1 |
Show 13 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES for SAP 16.0 | libssh2_org | 1.11.1-160000.5.1 | SUSE-SU-2026:23225-1, SUSE-SU-2026:23214-1 |
| SLES for SAP 15 SP6 | libssh2_org | 1.11.0-150600.20.6.1 | SUSE-SU-2026:3541-1 |
| SLES for SAP 15 SP5 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLES for SAP 15 SP4 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLES 16.0 | libssh2_org | 1.11.1-160000.5.1 | SUSE-SU-2026:23225-1, SUSE-SU-2026:23214-1 |
| SLE Micro 6.2 | libssh2_org | 1.11.1-160000.5.1 | SUSE-SU-2026:23049-1 |
| SLE Micro 6.1 | libssh2_org | 1.11.0-slfo.1.1_2.1 | SUSE-SU-2026:23187-1 |
| SLE Micro 6.0 | libssh2_org | 1.11.0-4.1 | SUSE-SU-2026:23245-1 |
| SLE Micro 5.5 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLE Micro 5.4 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLE Micro 5.3 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLE HPC 15 SP5 | libssh2_org | 1.11.0-150200.9.8.1 | SUSE-SU-2026:3526-1 |
| SLE HPC 15 SP4 | libssh2_org | 1.11.0-150000.4.35.1 | SUSE-SU-2026:4095-1, SUSE-SU-2026:3526-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | libssh2_org | 1.11.1-4.1 | openSUSE-SU-2026:11454-1 |
| openSUSE Leap 16.0 | libssh2_org | 1.11.1-160000.5.1 | openSUSE-SU-2026:21549-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | libssh2 | 1.11.1-r4 | — |
| Alpine v3.23 | libssh2 | 1.11.1-r4 | — |
| Alpine v3.22 | libssh2 | 1.11.1-r3 | — |
| Alpine v3.21 | libssh2 | 1.11.1-r3 | — |
Amazon Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Amazon Linux 2023 | cargo-c | 0.10.21-1.amzn2023.0.1 | ALAS2023-2026-2064 |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | libssh2 | 1.11.1-5 | — |
| Azure Linux 3 | rust | 1.96.1-2 | — |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | libssh2 +2 | No fix yet | — |
Advisories 15
- RHSA-2026:46927 Red Hat Security Advisory: Red Hat Hardened Images RPMs Security Update Red Hat Security Advisories (RHSA) · Oct 6, 2026
- WID-SEC-2026-2516 libssh2: Mehrere Schwachstellen BSI CERT-Bund (WID) · Sep 21, 2026
- SUSE-SU-2026:4095-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Sep 14, 2026
- USN-8722-1 libssh2 vulnerabilities Ubuntu Security Notices (USN) · Sep 3, 2026
- SUSE-SU-2026:23245-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 27, 2026
- SUSE-SU-2026:23225-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 27, 2026
- SUSE-SU-2026:23214-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 27, 2026
- SUSE-SU-2026:23187-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 26, 2026
- ALAS2023-2026-2064 Important: rust-cargo-c security update (Amazon Linux 2023) Amazon Linux Security Center (ALAS) · Aug 17, 2026
- openSUSE-SU-2026:21549-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 12, 2026
- SUSE-SU-2026:23049-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 12, 2026
- SUSE-SU-2026:3541-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 11, 2026
- SUSE-SU-2026:3525-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 8, 2026
- SUSE-SU-2026:3526-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 8, 2026
- openSUSE-SU-2026:11454-1 libssh2-1-1.11.1-4.1 on GA media SUSE / openSUSE Security Updates · Aug 6, 2026
References
- Pull Request issue-tracking patch
- Patch Commit patch
- https://www.vulncheck.com/advisories/libssh2-integer-underflow-dos-via-aes-gcm-cipher-negotiation third-party-advisory