CVE-2026-59843: A flaw was found in libssh

This month

MEDIUM 6.5WATCHLISTMITIGATEMITIGATEMITIGATE

CVE-2026-59843 is a medium-severity flaw (CVSS 6.5) affecting libssh, hardened images, enterprise linux. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 this priority

On your watchlist

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	6.5 (Medium)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	Low
User interaction	None
EPSS exploit chance	0.7% (top 46%)
CISA exploited list	No
Weakness	CWE-835, CWE-400
Published	2026-07-21
Last modified	2026-09-01

Publisher (CNA): Red Hat, Inc. · Vendor: libssh · redhat

Last updated 2026-09-01 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-07-21 12:18 UTCPublished CVE record published
2026-09-01 21:18 UTCUpdated Record last modified

libssh libssh MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy libssh || rpm -q libssh || libssh --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat hardened images MITIGATE

Affected: all versions

Fixed in: no fixed release known

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy hardened-images || rpm -q hardened-images || hardened-images --version

No fixed or unaffected release known

Apply the vendor mitigation from the advisory, disable the affected feature, or restrict network access.

redhat enterprise linux MITIGATE

Affected: 8.0 · 9.0 · 10.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 8.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-59843?

libssh: mitigate or apply the listed mitigation; hardened images: mitigate or apply the listed mitigation; enterprise linux: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-59843 being exploited?

CVE-2026-59843 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-59843 affect?

CVE-2026-59843 affects libssh, hardened images, enterprise linux. Severity is medium (CVSS 6.5). 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.

How urgent is CVE-2026-59843?

Priority 41/100. On your watchlist

Related CVEs

CVE-2026-59849 LOW 3.1 UPGRADE MITIGATE A flaw was found in libssh
CVE-2026-59842 LOW 3.7 DOWNGRADE MITIGATE A flaw was found in libssh
CVE-2026-15370 MEDIUM 6.7 UPGRADE MITIGATE A flaw was found in libssh
CVE-2026-59847 MEDIUM 5.9 UPGRADE MITIGATE A flaw was found in libssh
CVE-2026-59850 MEDIUM 4.3 MITIGATE MITIGATE A flaw was found in libssh

References

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