CVE-2026-49837 osrg CVE debrief

Who should care

Defenders responsible for BGP configuration and implementation, and those monitoring BGP sessions for unusual activity, should assess exposure and prioritize verification and remediation efforts. This includes network administrators, security teams, and IT professionals managing network infrastructure that utilizes GoBGP. These individuals should review the CVE record and NVD entry for detailed information and follow recommended actions to mitigate this  v

Why it matters

The BGP OPEN capability parsing issue in GoBGP versions prior to 4.6.0 can cause a malformed BGP OPEN message to be misinterpreted, potentially affecting peer AS validation during BGP session establishment. Defenders should prioritize verifying and upgrading to GoBGP version 4.6.0 or later, and monitoring BGP sessions for unusual activity.

• Peer AS validation may be affected during BGP session establishment
• BGP sessions may be vulnerable to malformed BGP OPEN messages

Technical summary

The BGP OPEN capability parsing issue in GoBGP versions prior to 4.6.0 can cause a malformed BGP OPEN message to be misinterpreted, potentially affecting peer AS validation during BGP session establishment. This issue arises from the parser incorrectly interpreting data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. The most security-relevant case is the 4-octet AS capability, where a capability with `CapLen == 0` may cause the parser to read bytes from the following capability as the 4-octet AS value.

Defensive priority

Defenders should prioritize verifying and upgrading to GoBGP version 4.6.0 or later, and monitoring BGP sessions for unusual activity.

Recommended defensive actions

• Verify and upgrade to GoBGP version 4.6.0 or later
• Monitor BGP sessions for unusual activity
• Review BGP configuration and implementation
• Perform vulnerability scanning to identify potentially affected systems
• Implement compensating controls for exposed systems
• Track exceptions and retest remediated assets
• Document evidence of remediation efforts

Evidence notes

The CVE record and NVD entry provide details on the BGP OPEN capability parsing issue in GoBGP. The issue is patched in version 4.6.0. Evidence from the CVE Program and NVD suggests that this vulnerability is specific to GoBGP versions prior to 4.6.0 and that defenders should verify and upgrade to the patched version. Additional verification tasks include reviewing BGP configuration and implementation, monitoring BGP sessions for unusual activity, and assessing potential exposure.

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.