CVE-2026-49838 in GoBGP
Summary
by MITRE • 09/11/2026
GoBGP is an open source Border Gateway Protocol (BGP) implementation in the Go Programming Language. Prior to version 4.7.0, GoBGP accepts a zero-length AS_PATH during UPDATE decoding and later panics while validating that attribute for a confederation eBGP peer. The vulnerable path is in the BGP UPDATE validator: a malformed UPDATE that should be rejected as a malformed AS_PATH instead reaches an unchecked `p.Value[0]` access, allowing a configured confederation eBGP peer to trigger a denial of service. Version 4.7.0 patches the issue.
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Analysis
by VulDB Data Team • 09/11/2026
GoBGP is a widely deployed open-source implementation of the Border Gateway Protocol written in the Go programming language, serving as a critical component for routing infrastructure across many internet service providers and enterprise networks. The vulnerability identified prior to version 4.7.0 represents a significant reliability risk within this software stack, specifically targeting the protocol state machine during the processing of BGP UPDATE messages. This flaw arises from an insufficient validation mechanism when handling Autonomous System path attributes in specific peering configurations involving confederations.
The technical root cause lies in the AS_PATH attribute parsing logic within the BGP UPDATE validator. According to RFC 4271, the AS_PATH is a sequence of autonomous system numbers that must contain at least one element; however, GoBGP versions prior to 4.7.0 failed to enforce this constraint strictly before proceeding with further validation steps for confederation eBGP peers. When a peer sends an UPDATE message containing a zero-length AS_PATH attribute, the software does not immediately reject it as malformed. Instead, execution continues into a subsequent validation block designed for confederations where the code attempts to access the first element of the path array using an unchecked index operation p.Value[0]. Because the array is empty due to the zero length, this direct memory access triggers a runtime panic in Go, causing the process to crash abruptly.
This behavior classifies as CWE-248: Uncaught Exception and CWE-119: Improper Restriction of Operations within the Bounds of a Memory Buffer, specifically manifesting as an out-of-bounds read that leads to application termination. From an operational perspective, this vulnerability enables a remote denial of service attack against any BGP router running vulnerable versions of GoBGP configured with confederation eBGP peers. An attacker or misconfigured peer can exploit this by sending specially crafted UPDATE messages containing empty AS_PATH attributes. The resulting panic causes the entire GoBGP process to terminate, leading to an immediate loss of routing connectivity for all prefixes learned through that session and potentially causing broader network instability if not handled by external monitoring or restart mechanisms.
The attack vector aligns with MITRE ATT&CK technique T1498: Network Denial of Service, specifically under the sub-technique of resource exhaustion via application crashes rather than bandwidth saturation. Since BGP is a control plane protocol essential for network reachability, disrupting it has severe consequences beyond simple service unavailability, including potential routing loops or black holes if alternative paths are not immediately available and reconverged.
Mitigation strategies primarily involve upgrading to GoBGP version 4.7.0 or later, where the developers have implemented proper bounds checking before accessing array elements within the confederation validation logic. For environments unable to upgrade immediately, network operators should implement strict ingress filtering on their border routers using route policies that reject UPDATE messages with invalid AS_PATH attributes based on length constraints defined in RFC 4271. Additionally, deploying BGP session authentication and monitoring tools can help detect anomalous traffic patterns indicative of exploitation attempts while maintaining operational resilience through redundant routing protocols or automatic restart scripts for the GoBGP daemon to minimize downtime duration during accidental crashes.