CVE-2026-121626 in GNU Gatekeeper
Summary
by MITRE • 11/03/2026
GNU Gatekeeper (gnugk) before 5.16 contains an out-of-bounds read vulnerability in H46024Socket::ReceivedProbePacket() that allows remote attackers to cause a heap over-read by sending short probe packets. Attackers can send a short application-defined RTCP packet to the media port during H.460.24 probing to read past the heap allocation and possibly crash the gatekeeper.
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Analysis
by VulDB Data Team • 11/03/2026
The GNU Gatekeeper, commonly referred to as gnugk, serves as a critical component in Voice over IP architectures by managing call admission control, address translation, and bandwidth management for H.323 endpoints. A significant security flaw has been identified within versions prior to 5.16 that affects the handling of probe packets during the H.460.24 signaling process. This vulnerability manifests as an out-of-bounds read operation located specifically within the ReceivedProbePacket method of the H46024Socket class. The root cause lies in insufficient validation of packet lengths before accessing memory buffers, allowing a remote attacker to exploit this logic error by transmitting malformed or undersized Real-time Transport Control Protocol packets designed for media port probing.
When an attacker sends a short application-defined RTCP packet during the H.460.24 probing phase, the software fails to verify that the incoming data fits within the allocated buffer boundaries. Consequently, the system attempts to read memory locations beyond the end of the heap allocation associated with the packet processing routine. This results in a heap over-read condition where sensitive information from adjacent memory regions may be exposed or processed incorrectly. The immediate operational impact includes potential denial of service through application crashes due to invalid memory access violations. In more severe scenarios, depending on the specific compiler and runtime environment, this out-of-bounds read could potentially leak confidential data stored in neighboring heap blocks, although exploitation for arbitrary code execution is less likely given the nature of a read-only vulnerability compared to write operations.
From a classification perspective, this flaw aligns with CWE-125, which describes Out-of-bounds Read vulnerabilities where software reads past the end of an allocated buffer. The attack vector leverages network accessibility, categorizing it under Remote Code Execution or Denial of Service contexts within threat modeling frameworks. Specifically, the exploitation technique relates to ATT&CK tactic T1078, Valid Accounts, if authenticated access is required for probing, or more broadly to reconnaissance and initial compromise techniques involving malformed packet injection. The vulnerability highlights a common pitfall in legacy VoIP implementations where strict adherence to protocol specifications regarding minimum packet sizes was not enforced during internal state machine transitions.
Mitigation strategies primarily involve upgrading the GNU Gatekeeper software to version 5.16 or later, where this boundary check has been corrected. For environments unable to upgrade immediately, network-level controls such as ingress filtering on media ports can help mitigate risk by restricting RTCP traffic from untrusted sources. Additionally, implementing strict input validation at the application layer for all incoming H.323 and related signaling packets is recommended to prevent similar logic errors in other components of the VoIP infrastructure. Security teams should also monitor system logs for unusual crash patterns or memory access violations associated with gnugk processes as an indicator of potential exploitation attempts.