Vulnerability · Published Sep 10, 2026 · Assigned by GitHub_M
CVE-2026-49837GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries
Medium 5.9
In plain English
A medium-severity out-of-bounds read in gobgp from osrg. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 27% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian:12 | gobgp | no fix listed | DEBIAN-CVE-2026-49837 |
| Debian:13 | gobgp | no fix listed | DEBIAN-CVE-2026-49837 |
| Debian:14 | gobgp | 4.6.0-1 | DEBIAN-CVE-2026-49837 |
| Go | github.com/osrg/gobgp/v4 | 4.6.0 | GO-2026-5955 |
| Go | github.com/osrg/gobgp/v4 | 4.6.0 | GHSA-gjrg-jjr3-56cm |
| Ubuntu:25.10 | gobgp | no fix listed | UBUNTU-CVE-2026-49837 |
| Ubuntu:26.10 | gobgp | no fix listed | UBUNTU-CVE-2026-49837 |
Affected products (as reported)
Weakness: CWE-125 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:H/A:N
References
- https://github.com/osrg/gobgp/security/advisories/GHSA-gjrg-jjr3-56cm x_refsource_CONFIRM
- https://github.com/osrg/gobgp/commit/f02ca397821f6ca182ef4eb492c3cbc459552d7c x_refsource_MISC