What’s Vulnerable › Vulnerabilities

CVE-2026-39834: Invoking infinite loop on large channel writes in golang.org/x/crypto/ssh

• Severity: critical (CVSS 9.1 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-05-22 · updated 2026-07-23
• Weakness: CWE-190

Description

When writing data larger than 4GB in a single Write call on an SSH channel, an integer overflow in the internal payload size calculation caused the write loop to spin indefinitely, sending empty packets without making progress. The size comparison now uses int64 to prevent truncation.

Affected products

• golang.org/x/crypto/ssh: before 0.52.0 — fixed in 0.52.0
• Golang.Org/X/Crypto: before 0.52.0 — fixed in 0.52.0

How to fix

Upgrade to a fixed version: golang.org/x/crypto/ssh 0.52.0; Golang.Org/X/Crypto 0.52.0. Check the vendor advisory for mitigations.

References

• https://go.dev/cl/781663
• https://go.dev/issue/79567
• https://groups.google.com/g/golang-announce/c/a082jnz-LvI
• https://pkg.go.dev/vuln/GO-2026-5020

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