CVE-2026-49838: GoBGP AS_PATH Validation Panic Due to Empty Attribute
Summary
CVE-2026-49838: GoBGP confederation validation panics on empty AS_PATH attribute. Affects github.com/osrg/gobgp/v4 versions < 4.7.0. Fixed in 4.7.0. How to fix ↓
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Background
GoBGP is an open-source implementation of the Border Gateway Protocol (BGP) used for inter-domain routing. It is designed to be efficient and flexible, allowing users to manage BGP sessions and routing policies. The package is widely used in networking applications and supports advanced features such as route reflection and confederation. However, it is susceptible to vulnerabilities that can lead to denial of service, as demonstrated by CVE-2026-49838.
Vulnerability Detail
The vulnerability arises from GoBGP's handling of the AS_PATH attribute during BGP UPDATE decoding. Specifically, when a zero-length AS_PATH is received from a confederation eBGP peer, the system panics due to an unchecked access to an empty value. This flaw allows an attacker to send a malformed UPDATE, causing a denial of service by crashing the receive goroutine and potentially terminating the process. The issue is rooted in the validation logic that fails to properly handle empty AS_PATH attributes, bypassing normal error handling mechanisms.
How To Fix
Latest published version: v4.10.0 as of 22 Oct 2026
go get github.com/osrg/gobgp/v4@v4.10.0Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
4.7.0
This is the first release that contains the fix.
go get github.com/osrg/gobgp/v4@v4.7.0Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
As a temporary workaround, you can implement additional validation checks in your BGP session management to reject UPDATE messages with zero-length AS_PATH attributes before they reach the GoBGP decoder. This can help prevent the panic from occurring until you can apply the official patch.
Conclusion
CVE-2026-49838 represents a significant vulnerability in GoBGP that can lead to denial of service through improper handling of AS_PATH attributes. It is crucial for users of GoBGP to update to the patched version 4.7.0 or later to mitigate this risk. Implementing additional validation checks can serve as a temporary workaround until the update is applied.
See every vulnerability recorded for github.com/osrg/gobgp/v4 →
FAQ
CVE-2026-49838 is a vulnerability in GoBGP that allows a remote unauthenticated peer to cause a denial of service by sending a malformed BGP UPDATE with an empty AS_PATH attribute.
If your GoBGP deployment is configured to accept eBGP connections from confederation peers, it may be vulnerable to this issue, which could lead to service interruptions.
Failing to address this vulnerability could result in denial of service, where your BGP sessions may crash, leading to network instability and potential downtime.
You can use Vulert's playground at Vulert Scanner to monitor and alert for open-source vulnerabilities in your software without requiring access to the code or installation.
The CVSS score for CVE-2026-49838 is 5.9, indicating a moderate severity level.
References
Related vulnerabilities
Recent vulnerabilities recorded for github.com/osrg/gobgp/v4.
