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medium · CVSS 6.5

CVE-2026-59843

Libssh: libssh: denial of service via zero advertised channel packet size

Published 21 Jul 2026 · Source updated 5 Nov 2026 · Retrieved 2026-11-05 22:56 UTC

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What happened?

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.

Description supplied by CVE Program. Formatting is simplified; follow the original advisory for full details.

Affected software and versions

Source-provided software and version information
SoftwareVersion informationFixed version
libsshRed Hatunaffected: 0:0.12.0-3.el10_2 to < *See vendor advisory
libsshRed Hatunaffected: 0:0.9.6-17.el8_10 to < *See vendor advisory
libsshRed Hatunaffected: 0:0.9.6-17.el8_10 to < *See vendor advisory
libsshRed Hatunaffected: 0:0.10.4-19.el9_8 to < *See vendor advisory
libsshRed Hatunaffected: 0:0.10.4-19.el9_8 to < *See vendor advisory
libssh-mainRed Hatunaffected: 0.12.1-4.hum1 to < *See vendor advisory

Version information comes from the source record and can include unaffected products and exceptions. Distribution packages may contain backported fixes: an older upstream version alone does not prove a server is affected.

Is it being exploited?

This CVE was not listed in the CISA catalogue at our last retrieval. This does not establish that exploitation is absent.

CISA data retrieved 2026-11-06 16:38 UTC. Check CISA ↗

How to respond

  1. Confirm the product, installed package version, and any configuration requirements in the vendor advisory.
  2. Follow the vendor’s remediation or workaround guidance in the references below. Structured fixed-version data is unavailable here; the publisher’s description may include a fix or workaround.
  3. Restart affected services if required, then verify the running version. Known exploitation may warrant investigation as well as patching.

Sources and remediation references

This public advisory does not determine whether a particular server is affected. Records are refreshed as sources change; verify urgent decisions against the original advisory.

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