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HIGH severity

GoBGP has Remote Denial of Service (Panic) via Malformed Well-known Path AttributeGHSA-7235-89m6-f4px

HIGH

GHSA-7235-89m6-f4px is a high-severity (CVSS 7.5) NULL Pointer Dereference vulnerability in github.com/osrg/gobgp/v4. A fix is available for github.com/osrg/gobgp/v4 — see the affected versions and patch details below.

Also known asCVE-2026-41642GO-2026-5198
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

  • CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
  • CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.

Exploitation and automatability from CISA’s SSVC triage for GHSA-7235-89m6-f4px.

EPSS Exploitation Probability

via FIRST.org ↗
0.5%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs43th percentile — riskier than 43% of all scored CVEsHighest risk
0.00%0.33%0.67%1.00%0.1%0.5%0.5%0.5%Jun 26Nov 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/osrg/gobgp/v4

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

A remote Denial of Service (DoS) vulnerability exists in GoBGP due to a nil pointer dereference. When a malformed BGP UPDATE message contains an unrecognized Path Attribute marked as "Well-known," the daemon fails to interrupt the message handling flow. This results in an illegal memory access and a full process crash (panic).

Details

The vulnerability is located in the Finite State Machine (FSM) message handling loop in pkg/server/fsm.go. According to RFC 4271, any Path Attribute with the Optional bit set to 0 is treated as "Well-known." If the Type Code is unrecognized, the BGP speaker MUST send a NOTIFICATION message.

In GoBGP v4.3.0, when such an attribute (e.g., Type 0xEE or 0xFF with flags 0x40) is received, the parsing layer identifies the error. However, the logic in recvMessageloop (around Line 1826) does not properly halt execution. It proceeds to reference the body of the parsed message. Because the message was deemed invalid during the initial attribute check, the body pointer is nil, leading to: panic: runtime error: invalid memory address or nil pointer dereference.

This bypasses the intended error-handling mechanism and causes the entire BGP daemon to terminate, rather than just closing the affected session.

panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x18 pc=0xc225e4]

goroutine 50 [running]:
github.com/osrg/gobgp/v4/pkg/server.(*fsmHandler).recvMessageloop(0x19f29bca92c0, {0x10069f0, 0x19f29bc48780}, {0x1014658, 0x19f29bc2a890}, 0x19f29baa0540, 0x19f29bc393b0, 0x19f29bc96cc0?)
        /home/base/Desktop/gobgp/pkg/server/fsm.go:1826 +0xa44
created by github.com/osrg/gobgp/v4/pkg/server.(*fsmHandler).established in goroutine 37
        /home/base/Desktop/gobgp/pkg/server/fsm.go:1916 +0x2d5
exit status 2

PoC

GoBGP Version: v4.3.0 Configure GoBGP with a neighbor (e.g., 192.168.31.195) in passive mode. Establish a standard BGP session (OPEN/KEEPALIVE exchange). Send a specifically crafted UPDATE packet containing an unrecognized Type Code marked as "Well-known" (Optional bit = 0). Payload 1 (Hex):

FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
00 17                # Length: 23
02                   # Type: UPDATE
00 00                # Withdrawn Routes Length: 0
00 04                # Total Path Attribute Length: 4     
40 EE 00             # Flag: 0x40 (Well-known, Transitive), Type: 0xEE (Unknown), Len: 0

Payload 2 (Hex):

FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF FF
00 17                # Length: 23
02                   # Type: UPDATE
00 00                # Withdrawn Routes Length: 0
00 04                # Total Path Attribute Length: 4     
40 01 01 00          # IGP Attribute
40 FF 00             # Flag: 0x40 (Well-known, Transitive), Type: 0xFF (Unknown), Len: 0

Impact

This vulnerability affects all GoBGP deployments peering with external or internal speakers. A single malformed UPDATE message from any peer can trigger a nil pointer dereference, causing the GoBGP daemon to panic and crash.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/osrg/gobgp/v4≥ 4.3.0&&< 4.4.04.4.0go get github.com/osrg/gobgp/v4@v4.4.0

Affected Products

1 product · 1 configurations
Application
gobgposrg
1 version
4.3.0

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/osrg/gobgp/v4, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/osrg/gobgp/v4 to 4.4.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-7235-89m6-f4px is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

### Summary A remote Denial of Service (DoS) vulnerability exists in GoBGP due to a nil pointer dereference. When a malformed BGP UPDATE message contains an unrecognized Path Attribute marked as "Well-known," the daemon fails to interrupt the message handling flow. This results in an illegal memory access and a full process crash (panic). ### Details The vulnerability is located in the Finite State Machine (FSM) message handling loop in pkg/server/fsm.go. According to RFC 4271, any Path Attribute with the Optional bit set to 0 is treated as "Well-known." If the Type Code is unrecognized, the
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