CVE-2026-56855: Previously, after a channel has been established, a malicious peer could send crafted messages that would dead

Q: How do I fix CVE-2026-56855?

crypto: upgrade to 0.56.0. Exact commands for each OS are on this page.

Q: Is CVE-2026-56855 being exploited?

CVE-2026-56855 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2026-56855 affect?

CVE-2026-56855 affects crypto. Severity is high (CVSS 7.5). Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all

Q: How urgent is CVE-2026-56855?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

This month

HIGH 7.5REMOTEUPGRADE

CVE-2026-56855 is a high-severity flaw (CVSS 7.5) affecting crypto. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all other messages as a protocol error and tear the connection down instead of buffering and blocking.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 57%)
CISA exploited list	No
Weakness	CWE-770
Published	2026-09-02
Last modified	2026-09-04

Publisher (CNA): Go Project · Vendor: golang

Last updated 2026-09-04 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-09-02 20:17 UTCPublished CVE record published
2026-09-04 16:34 UTCUpdated Record last modified

golang crypto UPGRADE

Affected: < 0.56.0

Fixed in: 0.56.0

Safe to downgrade to: no unaffected older release

1. Check installed version

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

2. UPGRADE to 0.56.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade crypto

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade crypto

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Advisories and coverage

Official advisories

Amazon Linux 2023 ALAS: ALAS2023-2026-3273 (important): containerd 2026-10-24
Amazon Linux 2023 ALAS: ALAS2023-2026-3274 (important): nerdctl 2026-10-24
Amazon Linux 2 ALAS: ALAS2DOCKER-2026-153 (important): containerd 2026-10-24
Amazon Linux 2 ALAS: ALAS2ECS-2026-145 (important): containerd 2026-10-24
Amazon Linux 2 ALAS: ALAS2-2026-4018 (important): nerdctl 2026-10-24
Amazon Linux 2 ALAS: ALAS2NITRO-ENCLAVES-2026-125 (important): containerd 2026-10-24

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-2026-56855?

crypto: upgrade to 0.56.0. Exact commands for each OS are on this page.

Is CVE-2026-56855 being exploited?

CVE-2026-56855 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-2026-56855 affect?

CVE-2026-56855 affects crypto. Severity is high (CVSS 7.5). Previously, after a channel has been established, a malicious peer could send crafted messages that would deadlock the entire connection. Now, we handle all RFC 4254 channel messages; global requests are handled explicitly. Then, treat all

How urgent is CVE-2026-56855?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Software pages

Go (Golang) vulnerabilities

Related CVEs

CVE-2026-78662 HIGH 7.5 UPGRADE Previously, a channel registered in the mux's chanList is not usable until it is established

References

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