CVE-2026-59843

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

Published Jul 21, 2026 CVSS 3.1 · 6.5 Medium EPSS < 1% KEV · Not listed
Description
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.

Remediation

Vendor Workaround

No workaround available.

Tracking

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Advisories

Source ID Title
Debian DLA Debian DLA DLA-4844-1 libssh security update
Debian DSA Debian DSA DSA-6410-1 libssh security update
Ubuntu USN Ubuntu USN USN-8699-1 libssh vulnerabilities
History
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
cpe:/a:redhat:enterprise_linux:8::appstream
cpe:/a:redhat:enterprise_linux:9::appstream
cpe:/o:redhat:enterprise_linux:8::baseos
cpe:/o:redhat:enterprise_linux:9::baseos
References
Type Values Removed Values Added
CPEs cpe:/o:redhat:enterprise_linux:10 cpe:/o:redhat:enterprise_linux:10.2
References
Type Values Removed Values Added
Weaknesses CWE-835
Type Values Removed Values Added
First Time appeared Libssh
Libssh libssh
Redhat hardened Images
Vendors & Products Libssh
Libssh libssh
Redhat hardened Images
Type Values Removed Values Added
Weaknesses CWE-400
Metrics ssvc

{'options': {'Automatable': 'no', 'Exploitation': 'none', 'Technical Impact': 'partial'}, 'version': '2.0.3'}

Type Values Removed Values Added
Description 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.
Title Libssh: libssh: denial of service via zero advertised channel packet size
First Time appeared Redhat
Redhat enterprise Linux
Redhat hummingbird
CPEs cpe:/a:redhat:hummingbird:1
cpe:/o:redhat:enterprise_linux:10
cpe:/o:redhat:enterprise_linux:8
cpe:/o:redhat:enterprise_linux:9
Vendors & Products Redhat
Redhat enterprise Linux
Redhat hummingbird
References
Metrics cvssV3_1

{'score': 6.5, 'vector': 'CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

Weaknesses

Sources

Status
PUBLISHED
Assigner
redhat
Published
Updated
Nov 5, 2026, 10:18 PM
Reserved
Jul 7, 2026, 3:40 PM
Status
Modified
Published
Jul 21, 2026, 12:18 PM
Modified
Sep 1, 2026, 9:18 PM
Severity
Moderate
Public date
Jul 21, 2026, 11:07 AM