A critical vulnerability (CVE-2025-43971) affecting GoBGP versions prior to 3.35.0 was disclosed on April 21, 2025. The flaw, which carries a CVSS score of 8.6 (High), allows unauthenticated attackers to trigger a denial-of-service condition by exploiting a zero-value input validation issue in the BGP packet handling logic. This vulnerability specifically resides in the pkg/packet/bgp/bgp.go file and can crash the service via a panic when processing malformed packets with a zero-length softwareVersionLen field1.
Technical Breakdown
The vulnerability stems from insufficient validation of the softwareVersionLen parameter in GoBGP’s BGP packet parsing logic. When a packet with a zero-length value for this field is processed, the service fails to handle the edge case, resulting in an uncontrolled panic. This behavior is classified under CWE-193 (Off-by-One Error)2. The issue was patched in commit 08a001e as part of the v3.35.0 release3.
Network-accessible GoBGP instances running versions below 3.35.0 are vulnerable to this attack. The impact is particularly severe in environments where GoBGP is used for critical routing infrastructure, as the panic can disrupt BGP peering sessions and potentially cause cascading network outages. The vulnerability requires no authentication and can be exploited by any system able to send BGP packets to the affected service.
Mitigation and Remediation
The primary mitigation is immediate upgrade to GoBGP version 3.35.0 or later. The patch properly validates the softwareVersionLen field before processing. For organizations unable to immediately upgrade, network-level controls should be implemented to restrict BGP packet sources to trusted peers only. Monitoring for unexpected service restarts or crashes in GoBGP instances can help detect potential exploitation attempts.
Related vulnerabilities in the same release include CVE-2025-43970 (MRT length validation flaw) and CVE-2025-43973 (buffer overflow vulnerability), though these carry lower CVSS scores4. Organizations should review all security fixes in the v3.35.0 release and assess their exposure to these additional issues.
Detection and Monitoring
Network monitoring solutions should be configured to alert on unexpected BGP session resets or service crashes. Log analysis should focus on identifying malformed BGP packets, particularly those with unusual length fields. The following indicators may suggest exploitation attempts:
- Unexpected GoBGP process crashes or restarts
- BGP packets with zero-length optional parameters
- Multiple connection attempts from single sources with malformed packets
The vulnerability was assigned by MITRE on April 21, 2025, with the CVSS v3.1 vector string AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H5. As of the disclosure date, no known active exploitation in the wild has been reported, but organizations should prioritize patching given the high severity and network-accessible nature of the vulnerability.
Conclusion
CVE-2025-43971 represents a significant risk to organizations using vulnerable versions of GoBGP for network routing. The combination of high severity, network accessibility, and potential for service disruption makes this vulnerability particularly concerning for critical infrastructure. Immediate patching is recommended, along with enhanced monitoring of BGP sessions and network traffic patterns. The GoBGP maintainers have provided clear guidance and fixes through their GitHub repository, making remediation straightforward for most deployments.
References
- “GoBGP Zero-Value Software Version Len Panic,” GitHub Advisory, Apr. 2025. [Online]. Available: https://github.com/osrg/gobgp/releases/tag/v3.35.0
- “CWE-193: Off-by-one Error,” MITRE, 2025. [Online]. Available: https://cwe.mitre.org/data/definitions/193.html
- “Fix for CVE-2025-43971,” GitHub Commit, Apr. 2025. [Online]. Available: https://github.com/osrg/gobgp/commit/08a001e06d90e8bcc190084c66992f46f62c0986
- “NVD – CVE-2025-43971,” NIST, Apr. 2025. [Online]. Available: https://nvd.nist.gov/vuln/detail/CVE-2025-43971
- “CVE-2025-43971,” MITRE CVE Entry, Apr. 2025. [Online]. Available: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2025-43971
