CVE-2026-49837: Osrg Gobgp

Medium severity, CVSS 5.9. EPSS: 0.3% chance of exploitation in the next 30 days.

GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Versions prior to 4.6.0 contain a BGP OPEN capability parsing issue where several concrete capability decoders may parse data from the full remaining capability buffer instead of the slice bounded by the declared capability length, `CapLen`. A malformed BGP OPEN message can cause bytes from a following capability to be interpreted as part of the current capability. 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. This parsed value may later affect peer AS validation during BGP session establishment. Version 4.6.0 patches the issue.

Affected products

• Osrg Gobgp: before 4.6.0 (fixed in 4.6.0)

Published 2026-09-10. Last modified 2026-09-16.