CVE-2026-39829 golang.org/x/crypto CVE debrief

Who should care

Defenders responsible for securing systems that use the golang.org/x/crypto/ssh package should assess their exposure to this vulnerability and take steps to mitigate it. This includes verifying the authenticity of public keys, limiting the size of RSA moduli and DSA parameters, and monitoring for potential denial-of-service attacks. Additionally, defenders should review compensating controls for exposed systems, check relevant monitoring and logs, and plan

Why it matters

CVE-2026-39829 is a high-severity vulnerability that can cause significant CPU consumption during signature verification, potentially leading to denial-of-service attacks. Defenders should prioritize verifying public key authenticity and limiting key sizes to mitigate this vulnerability.

• Potential denial-of-service attacks through high CPU consumption
• Increased risk of system crashes or performance degradation
• Need for verification of public key authenticity
• Priority for applying patches or updates

Technical summary

The RSA and DSA public key parsers in the golang.org/x/crypto/ssh package do not enforce size limits on key parameters, allowing for a crafted public key to cause high CPU consumption during signature verification. This can be triggered by unauthenticated clients during public key authentication, potentially leading to denial-of-service attacks. The issue has been addressed by limiting RSA moduli to 8192 bits and validating DSA parameters per FIPS 186-2. Defenders should prioritize verifying public key authenticity and limiting key sizes to mitigate this vulnerability.

Defensive priority

Defenders should prioritize verifying the authenticity of public keys and limiting the size of RSA moduli and DSA parameters to prevent potential denial-of-service attacks.

Recommended defensive actions

• Verify the authenticity of public keys
• Limit the size of RSA moduli and DSA parameters
• Monitor for potential denial-of-service attacks
• Apply patches or updates provided by the vendor
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented

Evidence notes

The CVE record and NVD vulnerability detail provide information on the vulnerability, its impact, and potential mitigations. Additional details can be found in the source references, including issue tracking and vendor advisories.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.