Description
libssh2 through 1.11.1, fixed in commit 1762685, contains a pre-authentication denial of service vulnerability in the SSH_MSG_EXT_INFO handler in src/packet.c that allows a malicious SSH server to cause a client CPU exhaustion loop by sending a crafted extension count value. A malicious server can set nr_extensions to 0xFFFFFFFF during key exchange, causing the client to spin in a tight CPU loop for over 60 seconds because return values from _libssh2_get_string() are unchecked and the session timeout does not apply to CPU-bound loops.
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 | 1.11.1-4 | — |
| Debian 13 | libssh2 | 1.11.1-1+deb13u1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.04 LTS | libssh2 | 1.11.1-1ubuntu0.26.04.2 | — |
| Ubuntu 25.10 | libssh2 | 1.11.1-1ubuntu0.25.10.2 | — |
| Ubuntu 24.04 LTS | libssh2 | 1.11.0-4.1ubuntu0.24.04.2 | — |
Red Hat
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Red Hat Hardened Images 1 | libssh2 +2 | 1.11.1-8.hum1 | RHSA-2026:29950 |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | libssh2_org | 1.11.0-150600.20.3.1 | SUSE-SU-2026:3076-1 |
| SLES 15 SP6 | libssh2_org | 1.11.0-150600.20.3.1 | SUSE-SU-2026:3076-1 |
| SLES 15 SP5 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLES 15 SP4 | libssh2_org | 1.11.0-150000.4.32.1 | SUSE-SU-2026:3082-1, SUSE-SU-2026:3074-1 |
| 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 | 1.11.1-160000.4.1 | SUSE-SU-2026:22364-1 |
| SLES for SAP 15 SP6 | libssh2_org | 1.11.0-150600.20.3.1 | SUSE-SU-2026:3076-1 |
| SLES for SAP 15 SP5 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLES for SAP 15 SP4 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLES 16.0 | libssh2_org | 1.11.1-160000.4.1 | SUSE-SU-2026:22364-1 |
| SLE Micro 6.2 | libssh2_org | 1.11.1-160000.4.1 | SUSE-SU-2026:22284-1 |
| 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 | 1.11.0-3.1 | SUSE-SU-2026:22438-1 |
| SLE Micro 5.5 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLE Micro 5.4 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLE Micro 5.3 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLE HPC 15 SP5 | libssh2_org | 1.11.0-150200.9.5.1 | SUSE-SU-2026:3074-1 |
| SLE HPC 15 SP4 | libssh2_org | 1.11.0-150000.4.32.1 | SUSE-SU-2026:3082-1, SUSE-SU-2026:3074-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | libssh2_org | 1.11.1-3.1 | openSUSE-SU-2026:11109-1 |
| openSUSE Leap 16.0 | libssh2_org | 1.11.1-160000.4.1 | openSUSE-SU-2026:21057-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | libssh2 | 1.11.1-r3 | — |
| Alpine v3.24 | rust +1 | 1.96.1-r0 | — |
| Alpine v3.23 | libssh2 | 1.11.1-r3 | — |
| Alpine v3.22 | libssh2 | 1.11.1-r2 | — |
| Alpine v3.21 | libssh2 | 1.11.1-r2 | — |
Azure Linux
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Azure Linux 3 | libssh2 | 1.11.1-4 | — |
| Azure Linux 3 | rust | No fix yet | — |
Wolfi
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Wolfi rolling | libssh2 +2 | 1.11.1-r7 | — |
Advisories 13
- RHSA-2026:29950 Red Hat Security Advisory: Red Hat Hardened Images RPMs bug fix and enhancement update Red Hat Security Advisories (RHSA) · Oct 20, 2026
- WID-SEC-2026-1996 libssh2: Mehrere Schwachstellen BSI CERT-Bund (WID) · Aug 31, 2026
- SUSE-SU-2026:23187-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 26, 2026
- SUSE-SU-2026:3525-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Aug 8, 2026
- SUSE-SU-2026:3076-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jul 17, 2026
- SUSE-SU-2026:3082-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jul 17, 2026
- SUSE-SU-2026:3074-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jul 17, 2026
- SUSE-SU-2026:22438-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jul 3, 2026
- SUSE-SU-2026:22364-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jul 2, 2026
- SUSE-SU-2026:22284-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jun 30, 2026
- openSUSE-SU-2026:21057-1 Security update for libssh2_org SUSE / openSUSE Security Updates · Jun 30, 2026
- NCSC-2026-0210 Kwetsbaarheden verholpen in libssh2 door libssh NCSC-NL (Netherlands) · Jun 24, 2026
- openSUSE-SU-2026:11109-1 libssh2-1-1.11.1-3.1 on GA media SUSE / openSUSE Security Updates · Jun 24, 2026
References
- Pull Request issue-tracking patch
- Patch Commit patch
- https://www.vulncheck.com/advisories/libssh2-pre-authentication-dos-via-ssh-msg-ext-info-handler third-party-advisory