CVE-2026-37462 Overview
CVE-2026-37462 is an integer underflow vulnerability in GoBGP v4.3.0, an open-source Border Gateway Protocol (BGP) implementation written in Go. The flaw resides in the BGPUpdate.DecodeFromBytes function within /bgp/bgp.go. Attackers can trigger the condition by sending a crafted BGP UPDATE message to a vulnerable peer. Successful exploitation causes a Denial of Service (DoS) against the GoBGP process, disrupting routing operations.
Critical Impact
A remote, unauthenticated attacker capable of establishing or hijacking a BGP session can crash the GoBGP daemon, impacting network availability and route propagation.
Affected Products
- GoBGP v4.3.0
- Network infrastructure relying on GoBGP for BGP routing
- Systems using the affected /pkg/packet/bgp/bgp.go packet decoder
Discovery Timeline
- 2026-06-03 - CVE-2026-37462 published to NVD
- 2026-06-03 - Last updated in NVD database
Technical Details for CVE-2026-37462
Vulnerability Analysis
The vulnerability is an integer underflow [CWE-191] in the BGP UPDATE message decoder of GoBGP. The BGPUpdate.DecodeFromBytes function parses untrusted bytes received over a BGP session. When length fields in the crafted UPDATE message are smaller than expected header sizes, subtraction operations underflow. The resulting wraparound produces an unexpectedly large unsigned value used in subsequent length checks or slice operations. This leads to out-of-bounds access or excessive memory allocation, causing the GoBGP process to panic and terminate.
BGP UPDATE messages carry Network Layer Reachability Information (NLRI) and path attributes. The decoder calculates remaining buffer sizes by subtracting consumed bytes from declared lengths. Without sufficient bounds validation, a peer can declare a malformed length to drive the calculation below zero.
Root Cause
The root cause is missing validation of length fields before performing arithmetic on unsigned integers in the BGP UPDATE parser. The decoder trusts attacker-controlled length values from the wire and does not verify that declared lengths fit within the remaining buffer before subtraction.
Attack Vector
The attack requires network access to a GoBGP listener and the ability to complete or hijack a BGP session with the target. Once a session is established, the attacker sends a malformed BGP UPDATE message containing crafted length fields. No authentication beyond standard BGP peering is required when an attacker controls a peer. The underflow triggers a runtime panic in Go, terminating the routing daemon. Refer to the GitHub GoBGP commit log and GoBGP source code for the affected code paths.
Detection Methods for CVE-2026-37462
Indicators of Compromise
- Unexpected termination or panic logs from the GoBGP daemon referencing BGPUpdate.DecodeFromBytes or bgp.go
- BGP session resets followed by route withdrawal events from monitored peers
- Inbound BGP UPDATE messages with malformed or inconsistent length fields
Detection Strategies
- Inspect BGP traffic with protocol-aware sensors to flag UPDATE messages where declared lengths are inconsistent with packet size
- Correlate GoBGP process crashes with recent inbound BGP UPDATE activity from specific peers
- Monitor system logs for repeated GoBGP restarts and Go runtime panic traces
Monitoring Recommendations
- Centralize GoBGP stdout, stderr, and systemd journal logs for crash detection
- Track BGP session uptime metrics and alert on abnormal session resets
- Capture pcap samples of BGP traffic from untrusted peers for forensic analysis
How to Mitigate CVE-2026-37462
Immediate Actions Required
- Upgrade GoBGP to a patched release that includes commit 9ce8936672ebc07df524da77fa4c6ae26d92be6d or later
- Restrict BGP peering to authenticated, trusted neighbors using TCP-AO or MD5 authentication
- Apply access control lists to limit TCP port 179 exposure to known peer addresses
Patch Information
The GoBGP maintainers addressed the integer underflow in commit 9ce8936672ebc07df524da77fa4c6ae26d92be6d. Operators running GoBGP v4.3.0 should rebuild from a fixed commit or upgrade to a release containing the patch. See the GitHub GoBGP commit log for the code change.
Workarounds
- Filter BGP sessions at the network edge to allow connections only from explicitly trusted peer IP addresses
- Deploy process supervision such as systemd with automatic restart to reduce downtime when the daemon crashes
- Use BGP route validation and prefix filters at upstream devices to limit exposure from compromised peers
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
