GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries (CVE-2026-49837) | HOL Guard CVE

Medium severityCVE-2026-49837GHSA-GJRG-JJR3-56CM

GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries

Answer in brief

CVE-2026-49837 records a Medium severity vulnerability in GoBGP: BGP OPEN capability parser may read capability values outside declared CapLen boundaries. The current sources do not mark it as known exploited. The current feed maps osrg/gobgp (generic), github.com/osrg/gobgp/v4 (go). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Sep 10, 2026Updated Sep 15, 2026Source checked Sep 17, 2026First seen by HOL Jul 10, 2026Material review Sep 15, 2026

Upstream Advisory

Key facts

Risk: Medium
Exploitation: Not marked as known exploited
Affected software: 2 mapped packages or products
Fix availability: Available

Why this deserves its current priority

A CVSS score is not reported in the current record. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps osrg/gobgp (generic), github.com/osrg/gobgp/v4 (go). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
Package	Affected range	Fixed version
osrg/gobgpgeneric	< 4.6.0	Not reported
github.com/osrg/gobgp/v4go	<=4.5.0	4.6.0

Recommended response

Check inventory. Check lockfiles and deployed manifests for osrg/gobgp, github.com/osrg/gobgp/v4.
Review the reported fix. Update github.com/osrg/gobgp/v4 to 4.6.0 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

Published upstream
Sep 10, 2026
Evidence: source:cvelist:source_dates:source-dates:record
Source modified
Sep 15, 2026
Evidence: source:cvelist:source_dates:source-dates:record
First seen by HOL
Jul 10, 2026

Sources and claim methodology

Upstream source 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.

Quoted source text, attributed separately from HOL analysis.