Libssh: libssh: denial of service via zero advertised channel packet size
Priority LOW 30CWE-835Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · High
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-835.
Summary
A flaw was found in libssh. A remote authenticated peer can advertise a zero maximum packet size in SSH_MSG_CHANNEL_OPEN, causing later channel writes to loop indefinitely and consume CPU, leading to denial of service.
Why it matters now
Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00567 47th percentileScored 2026-11-07
Fix Fixed Red Hat: 4 advisories
SSVC decision points
CISA ADP · SSVC 2.0.3
- Exploitation
- None
- Automatable
- No
- Technical impact
- Partial
The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| Red Hat | Red Hat Enterprise Linux 10 | — | 0.12.0-3.el10_2 | Patch available | CNA |
| Red Hat | Red Hat Enterprise Linux 8 | — | 0.9.6-17.el8_10 | Patch available | CNA |
| Red Hat | Red Hat Enterprise Linux 8 | — | 0.9.6-17.el8_10 | Patch available | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | 0.10.4-19.el9_8 | Patch available | CNA |
| Red Hat | Red Hat Enterprise Linux 9 | — | 0.10.4-19.el9_8 | Patch available | CNA |
| Red Hat | Red Hat Hardened Images | — | 0.12.1-4.hum1 | Patch available | CNA |
- Red Hat Enterprise Linux 10 VendorRed Hat Affected — Fixed in 0.12.0-3.el10_2 Patch available CNA
- Red Hat Enterprise Linux 8 VendorRed Hat Affected — Fixed in 0.9.6-17.el8_10 Patch available CNA
- Red Hat Enterprise Linux 8 VendorRed Hat Affected — Fixed in 0.9.6-17.el8_10 Patch available CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in 0.10.4-19.el9_8 Patch available CNA
- Red Hat Enterprise Linux 9 VendorRed Hat Affected — Fixed in 0.10.4-19.el9_8 Patch available CNA
- Red Hat Hardened Images VendorRed Hat Affected — Fixed in 0.12.1-4.hum1 Patch available CNA
CPE configurations NVD · 5
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:libssh:libssh:-:*:*:*:*:*:*:* | not specified by NVD | Vulnerable | libssh |
| cpe:2.3:a:redhat:hardened_images:-:*:*:*:*:*:*:* | not specified by NVD | Vulnerable | Red Hat |
| cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* | 8.0 | Vulnerable | Red Hat |
| cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:* | 9.0 | Vulnerable | Red Hat |
| cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:* | 10.0 | Vulnerable | Red Hat |
- cpe:2.3:a:libssh:libssh:-:*:*:*:*:*:*:* Versions not specified by NVD Vulnerable ·libssh
- cpe:2.3:a:redhat:hardened_images:-:*:*:*:*:*:*:* Versions not specified by NVD Vulnerable ·Red Hat
- cpe:2.3:o:redhat:enterprise_linux:8.0:*:*:*:*:*:*:* Versions 8.0 Vulnerable ·Red Hat
- cpe:2.3:o:redhat:enterprise_linux:9.0:*:*:*:*:*:*:* Versions 9.0 Vulnerable ·Red Hat
- cpe:2.3:o:redhat:enterprise_linux:10.0:*:*:*:*:*:*:* Versions 10.0 Vulnerable ·Red Hat
Remediation
Red Hat 4 advisories
- RHSA-2026:62218 Released 2026-09-01 · Red Hat rating Moderatelibssh security update
- Red Hat Enterprise Linux AppStream (v. 8) libssh-devel-0.9.6-17.el8_10
- Red Hat Enterprise Linux BaseOS (v. 8) libssh-0.9.6-17.el8_10, libssh-config-0.9.6-17.el8_10
- RHSA-2026:62217 Released 2026-09-01 · Red Hat rating Moderatelibssh security update
- Red Hat Enterprise Linux AppStream (v. 9) libssh-devel-0.10.4-19.el9_8
- Red Hat Enterprise Linux BaseOS (v. 9) libssh-0.10.4-19.el9_8, libssh-config-0.10.4-19.el9_8
- RHSA-2026:55855 Released 2026-08-17 · Red Hat rating Importantlibssh security update
- Red Hat Enterprise Linux AppStream (v. 10) libssh-devel-0.12.0-3.el10_2
- Red Hat Enterprise Linux BaseOS (v. 10) libssh-0.12.0-3.el10_2, libssh-config-0.12.0-3.el10_2
Show 1 more Red Hat advisories
- RHSA-2026:42922 Released 2026-07-21 · Red Hat rating ImportantRed Hat Hardened Images RPMs bug fix and enhancement update
- Red Hat Hardened Images libssh-0.12.1-4.hum1@aarch64, libssh-0.12.1-4.hum1@src, libssh-0.12.1-4.hum1@x86_64 +4
Fixed in the same release
Records fixed by the same vendor advisory or release, as the CNA lists them.
- Advisory ·
Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and 2 more products — RHSA-2026:55855
11 records Highest priority Priority MEDIUM 1 MEDIUM, 10 LOW
Other records, highest priority first
- TI-2026-42667 Libssh: libssh: authentication bypass via missing gssapi principal checkPriority MEDIUM 41
- TI-2026-42663 Libssh: libssh: integrity downgrade via openssl aes-gcm tag verificationPriority LOW 39
- TI-2026-42666 Libssh: libssh: use-after-free via data callbacks on closed channelsPriority LOW 33
- Advisory ·
Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and 2 more products — RHSA-2026:42922
10 records Highest priority Priority MEDIUM 1 MEDIUM, 9 LOW
Other records, highest priority first
- TI-2026-42667 Libssh: libssh: authentication bypass via missing gssapi principal checkPriority MEDIUM 41
- TI-2026-42663 Libssh: libssh: integrity downgrade via openssl aes-gcm tag verificationPriority LOW 39
- TI-2026-42666 Libssh: libssh: use-after-free via data callbacks on closed channelsPriority LOW 33
Show 2 more groups
- Advisory ·
Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and 2 more products — RHSA-2026:62217
7 records Highest priority Priority LOW 7 LOW
Other records, highest priority first
- TI-2026-42663 Libssh: libssh: integrity downgrade via openssl aes-gcm tag verificationPriority LOW 39
- TI-2026-42666 Libssh: libssh: use-after-free via data callbacks on closed channelsPriority LOW 33
- TI-2026-42664 Libssh: libssh: denial of service via sftp responses with unknown request idsPriority LOW 30
- Advisory ·
Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8 and 2 more products — RHSA-2026:62218
7 records Highest priority Priority LOW 7 LOW
Other records, highest priority first
- TI-2026-42663 Libssh: libssh: integrity downgrade via openssl aes-gcm tag verificationPriority LOW 39
- TI-2026-42666 Libssh: libssh: use-after-free via data callbacks on closed channelsPriority LOW 33
- TI-2026-42664 Libssh: libssh: denial of service via sftp responses with unknown request idsPriority LOW 30
Vendor assessments
Red Hat
Red Hat rating: Moderate. Red Hat's page for this CVE →
| Product | Status | Plan or fix |
|---|---|---|
| Red Hat Enterprise Linux AppStream (v. 10) | Fixed | RHSA-2026:55855 |
| Red Hat Enterprise Linux AppStream (v. 8) | Fixed | RHSA-2026:62218 |
| Red Hat Enterprise Linux AppStream (v. 9) | Fixed | RHSA-2026:62217 |
| Red Hat Enterprise Linux BaseOS (v. 10) | Fixed | RHSA-2026:55855 |
| Red Hat Enterprise Linux BaseOS (v. 8) | Fixed | RHSA-2026:62218 |
| Red Hat Enterprise Linux BaseOS (v. 9) | Fixed | RHSA-2026:62217 |
| Red Hat Hardened Images | Fixed | RHSA-2026:42922 |
Timeline
- 2026-10-02 Threatist record created from CVE-2026-59843
- 2026-10-03 Alias added: GHSA-4846-7xwg-pw5m
- 2026-10-28 EPSS moved to the below the 50th percentile
References
More Red Hat Enterprise Linux vulnerabilities
- TI-2019-08259 Underflow in PHP-FPM can lead to RCE KEVCVSS 3.1CRITICAL 9.8
- TI-2018-10530 Code injection in [UNKNOWN] RichFaces KEVCVSS 3.1CRITICAL 9.8
- TI-2014-05975 GNU Bash through 4.3 bash43-025 processes trailing strings after certain malformed… KEVCVSS 3.1CRITICAL 9.8
- TI-2014-05157 GNU Bash through 4.3 processes trailing strings after function definitions in the values… KEVCVSS 3.1CRITICAL 9.8
- TI-2025-23530 Sudo before 1.9.17p1 allows local users to obtain root access because /etc/nsswitch.conf… KEVCVSS 3.1CRITICAL 9.3
- TI-2021-17490 mod_proxy SSRF KEVCVSS 3.1CRITICAL 9.0
Sources
- CVE-2026-59843 · CVE Program
- CVE-2026-59843 · NVD
- FIRST EPSS
- GHSA-4846-7xwg-pw5m · GitHub Advisory Database · CC BY 4.0
- CVE-2026-59843 · Red Hat security data · CC BY 4.0
This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences