Security Digest · Vulnerability record
CVE-2026-39834: golang.org/x/crypto vulnerable to infinite loop on large channel writes
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.
CVSS 9.1 Critical EPSS 0.6% · p50
Should you act?
Critical and remotely reachable
No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.
- No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
- EPSS 0.6%, percentile 50: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 50% of all scored CVEs (low). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes
golang.org/x/crypto(Go) < 0.52.0, fixed in 0.52.0. Check your lockfile, including transitive dependencies.
What it is
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.
From the GitHub advisory
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.
Weakness type: CWE-190.
Product: golang.org/x/crypto (Go) · Assigned by: Go · Published: 2026-05-22
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | golang.org/x/crypto | < 0.52.0 | 0.52.0 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| golang.org/x/crypto | golang.org/x/crypto/ssh | < 0.52.0 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| CISA-ADP | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H |
- Attack vector: network (remotely reachable)
- Attack complexity: low
- Privileges required: none (no login)
- User interaction: none
- Scope: unchanged
CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.
Exploitation and urgency
- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation none, automatable yes, technical impact partial.
- FIRST EPSS (model of 2026-10-21): 0.64% probability of exploitation activity in the next 30 days; percentile 50.
Timeline
- — CVE record last updated
- — CVE record published by Go
- — GitHub-reviewed advisory GHSA-rm3j-f69w-wqmq published (critical)
Sources and references
Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.
Vulnerability records
- GitHub Advisory GHSA-rm3j-f69w-wqmq github.com
- CVE.org record CVE-2026-39834 cve.org
- NVD entry CVE-2026-39834 nvd.nist.gov
Other references from the CVE record and advisory
- go.dev go.dev
- groups.google.com groups.google.com
- go.dev go.dev
- pkg.go.dev pkg.go.dev