CVE-2026-56855

⚠️ high

Summary

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.

CVSS Score

7.5

High

EPSS Score

0.4

Exploit Probability

Published Date

2026-09-02

First Seen: 2026-09-03

📊 Relative Risk Intelligence

This CVE is Moderate Risk - more severe than 67.8% of all 360,673 vulnerabilities in our database.

#116,318

Above average severity

Severity Percentile

🎯 CISA SSVC Assessment Updated: Sep 3, 2026

🔍 Exploitation Status

None

No known exploits

⚙️ Automatable

YES

Can be exploited automatically

💥 Technical Impact

Partial

Limited system impact

🏆 Discovered By

Will Mortensen

SSVC data provided by CISA

Last Modified 2026-09-04

Source NVD 🔗

CVSS Vector 3.1 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CWE IDs (Weakness Types)

CWE-770

📦 Affected Products 1

Vendor	Product	Status	Affected Versions
golang	crypto	Affected	< 0.56.0

🔗 References 4

https://go.dev/cl/826524

Patch

https://go.dev/issue/81317

Issue Tracking Vendor Advisory

https://groups.google.com/g/golang-announce/c/1y3fb2...

Mailing List Vendor Advisory

https://pkg.go.dev/vuln/GO-2026-6355

Vendor Advisory

🔗 Related CVEs 6

CVE ID	Severity	CVSS	EPSS	Summary	Published
CVE-2026-78662	⚠️ high	7.5	0.3	Previously, a channel registered in the mux's chanList is not usable until it is established. A malicious peer was able ...	2026-09-02
CVE-2026-39827	🔶 medium	6.5	0.3	An authenticated SSH client that repeatedly opened channels which were rejected by the server caused unbounded memory gr...	2026-05-22
CVE-2026-39828	🔶 medium	6.3	0.4	When an SSH server authentication callback returned PartialSuccessError with non-nil Permissions, those permissions were...	2026-05-22
CVE-2026-39829	⚠️ high	7.5	0.5	The RSA and DSA public key parsers did not enforce size limits on key parameters. A crafted public key with an excessive...	2026-05-22
CVE-2026-39830	⛔ critical	9.1	0.6	A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection...	2026-05-22
CVE-2026-39831	⛔ critical	9.1	0.4	The Verify() method for FIDO/U2F security key types (sk-ecdsa-sha2-nistp256@openssh.com, sk-ssh-ed25519@openssh.com) did...	2026-05-22

These CVEs affect the same products