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Not in CISA KEV
CRITICAL severity

CVE-2026-39830 — x/crypto

CRITICAL

CVE-2026-39830 is a critical-severity (CVSS 9.1) Buffer Overflow vulnerability in golang.org/x/crypto. A fix is available for golang.org/x/crypto — see the affected versions and patch details below.

Invoking client can cause server deadlock on unexpected responses in golang.org/x/crypto/ssh

Also known asGHSA-vgwf-h737-ff37GO-2026-5017
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 23, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-39830.

EPSS Exploitation Probability

via FIRST.org ↗
0.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs49th percentile — riskier than 49% of all scored CVEsHighest risk
0.00%0.37%0.75%1.12%0.1%0.6%Jun 26Sep 26Oct 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-39830 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 395,249 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐹golang.org/x/crypto

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogolang.org/x/cryptoall versions0.52.0go get golang.org/x/crypto@v0.52.0

Affected Products

1 product · 1 configurations
Application
cryptogolang
< 0.52.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for golang.org/x/crypto, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update golang.org/x/crypto to 0.52.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-39830 is resolved across your whole dependency graph.

  3. Workarounds

    Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This is an Important denial of service flaw in `golang.org/x/crypto/ssh`. A remote, unauthenticated attacker can exploit this vulnerability by sending unsolicited global request responses to an affected SSH server, leading to resource exhaustion and a denial of service. The impact is considered Important due to the…

Workaround published by Red Hat
To mitigate this denial of service vulnerability, restrict network access to any service that utilizes the `golang.org/x/crypto/ssh` library and is exposed to untrusted networks. Implement firewall rules to allow connections only from trusted hosts or networks. This action limits the ability of malicious peers to send unsolicited global request responses. A restart of the affected service may be necessary for the new network rules to be applied effectively.
Source: Red Hat security advisory for CVE-2026-39830 (CC BY 4.0)
ProductFixed inAdvisory
Cryostat 4 on RHEL 9cryostat/cryostat-storage-rhel9:4.2.0-19RHSA-2026:48151
Red Hat Enterprise Linux 10buildah-2:1.43.1-3.el10_2RHSA-2026:36199
Red Hat Enterprise Linux 10podman-7:5.8.2-4.el10_2RHSA-2026:37072
Red Hat Enterprise Linux 8container-tools:rhel8-8100020260701102925.afee755dRHSA-2026:35833
Red Hat Enterprise Linux 8.8 Telecommunications Update Servicecontainer-tools:rhel8-8080020260721142025.63b34585RHSA-2026:49944
Red Hat Enterprise Linux 9buildah-2:1.43.1-2.el9_8RHSA-2026:29455
Red Hat Enterprise Linux 9podman-6:5.8.2-7.el9_8RHSA-2026:69961
Red Hat Enterprise Linux 9.6 Extended Update Supportpodman-5:5.4.0-22.el9_6.5RHSA-2026:67450
UbuntuCRITICAL
USN-8447-2UbuntuUSN-8447-3Ubuntu

Frequently Asked Questions

A malicious SSH peer could send unsolicited global request responses to fill an internal buffer, blocking the connection's read loop. The blocked goroutine could not be released by calling Close(), resulting in a resource leak per connection. Unsolicited global responses are now discarded.
O3 Security · Impact-Aware SCA

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CVE-2026-39830: x/crypto — Fixed in 0.52.0