CVE-2026-72253 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
netfilter: nf_conntrack_sip: validate skb_dst() before accessing it
tc ingress and openvswitch do not guarantee routing information to be available. These subsystems use the conntrack helper infrastructure, and the SIP helper relies on the skb_dst() to be present if sip_external_media is set to 1 (which is disabled by default as a module parameter).
This effectively disables the sip_external_media toggle for these subsystems without resulting in a crash.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability resides in the Linux kernel's netfilter subsystem, specifically within the nf_conntrack_sip module that handles Session Initiation Protocol connection tracking. This flaw represents a critical issue in kernel space memory management and object validation where the system fails to properly verify the existence of routing information before attempting to access it. The vulnerability manifests when the sip_external_media parameter is enabled, which triggers the SIP helper to rely on skb_dst() function calls to determine external media addresses for session negotiation.
The technical root cause stems from improper validation of network packet metadata within the conntrack infrastructure. When tc ingress and openvswitch subsystems process packets, they do not guarantee that routing information will be available in the sk_buff structure's destination field. These subsystems utilize the conntrack helper framework but operate without maintaining consistent routing context, creating a scenario where the SIP helper assumes routing data exists when it may not. The vulnerability occurs because the code path does not perform proper null checking or validation of the skb_dst() return value before dereferencing it.
This weakness directly impacts system stability and security posture by potentially causing kernel memory corruption or invalid memory access patterns that could be exploited by malicious actors. The flaw affects systems running Linux kernels with netfilter and conntrack functionality, particularly those utilizing tc ingress or openvswitch networking components. The vulnerability does not result in immediate crashes but rather silently disables the sip_external_media toggle functionality, effectively rendering a security feature non-operational without alerting administrators to the underlying issue.
From an operational perspective, this vulnerability creates a false sense of security where administrators believe external media handling is properly configured when it remains disabled due to the validation failure. The impact extends beyond simple functional degradation to potential denial of service conditions in VoIP environments where proper media address negotiation is critical for call establishment and maintenance. Organizations using Linux-based network appliances, firewalls, or VoIP gateways that rely on these subsystems face increased risk of communication failures and potential security gaps.
The vulnerability aligns with CWE-476 which addresses NULL pointer dereference conditions in software systems, and demonstrates characteristics consistent with ATT&CK technique T1059.007 for kernel-level exploitation pathways. Mitigation strategies should focus on ensuring proper null validation before accessing routing information, implementing robust error handling in network subsystems, and maintaining updated kernel versions that include the fix. System administrators should verify their kernel configurations and consider disabling the sip_external_media parameter if tc ingress or openvswitch are actively used, while also monitoring for potential memory access violations in network processing components.