CVE-2026-72398 in Linux
Summary
by MITRE • 08/15/2026
In the Linux kernel, the following vulnerability has been resolved:
sctp: add INIT verification after cookie unpacking
In SCTP handshake, the INIT chunk is initially processed by the server and embedded into the cookie carried in INIT-ACK. The client then returns this cookie via COOKIE-ECHO, where the server unpacks it and reconstructs the original INIT chunk.
When cookie authentication is enabled, the cookie contents are protected against tampering, so reusing the unpacked INIT without re-verification is safe.
However, when cookie authentication is disabled, the reconstructed INIT can no longer be trusted. In this case, the INIT must be explicitly validated after unpacking to avoid processing potentially tampered data.
Add sctp_verify_init() checks after cookie unpacking in COOKIE-ECHO processing paths (sctp_sf_do_5_1D_ce() and sctp_sf_do_5_2_4_dupcook()) when cookie_auth_enable is disabled. On failure, the new association is freed and the packet is discarded.
Also tighten cookie validation in sctp_unpack_cookie() by verifying the embedded chunk type is SCTP_CID_INIT before treating it as an INIT chunk.
Finally, update sctp_verify_init() to validate parameter bounds using the actual embedded INIT length instead of chunk->chunk_end, since the INIT stored in COOKIE-ECHO may not span the entire chunk buffer.
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Analysis
by VulDB Data Team • 08/15/2026
The vulnerability addressed in this linux kernel security patch relates to a critical flaw in the stream control transmission protocol sctp implementation that could allow for malicious data manipulation during association establishment. This issue specifically affects the cookie echo processing mechanism where the server reconstructs an initialisation chunk from embedded cookie data received from clients. The problem arises from insufficient validation of reconstructed data when cookie authentication is disabled, creating potential attack vectors for remote code execution or denial of service conditions.
The technical flaw stems from the sctp protocol's handling of cookie echo messages during the handshake process where the server unpacks previously embedded init chunks without proper re-validation. When cookie authentication is enabled, the system correctly trusts the protected cookie contents and avoids re-verification, but when disabled, the reconstructed init chunk becomes vulnerable to manipulation. The vulnerability exists in two primary processing paths within the sctp subsystem: sctp_sf_do_5_1D_ce() and sctp_sf_do_5_2_4_dupcook() functions that handle different types of cookie echo scenarios. These functions previously failed to perform explicit verification of init parameters after unpacking, allowing potentially malicious data to proceed through the normal association establishment flow.
The operational impact of this vulnerability extends across multiple cybersecurity frameworks and attack vectors, particularly aligning with attack techniques described in the attack tree framework where an attacker could exploit the missing validation step to inject malformed data. This weakness creates opportunities for privilege escalation attacks and resource exhaustion conditions that could affect network service availability. The vulnerability directly relates to common weakness enumeration cwe-254 which describes security features that are insufficiently protected against manipulation, and it aligns with attack patterns in the mitre attack framework where adversaries exploit missing input validation controls during protocol negotiation phases.
The mitigation strategy implemented in this patch addresses the core issue by introducing explicit init verification checks after cookie unpacking when authentication is disabled. The solution requires calling sctp_verify_init() function in two specific processing paths to validate init chunk parameters before proceeding with association establishment. When verification fails, the system properly cleans up resources and discards the malicious packet rather than continuing processing with potentially tampered data. Additionally, the patch strengthens cookie validation within sctp_unpack_cookie() by ensuring that embedded chunk types are explicitly verified as SCTP_CID_INIT before treating them as init chunks, preventing type confusion attacks.
The enhanced verification mechanism also improves parameter bounds checking within sctp_verify_init() to use actual embedded init length rather than relying on chunk->chunk_end which could be misleading when the init data doesn't span the complete chunk buffer. This refinement prevents potential buffer overflow conditions that could occur during parameter validation and ensures proper memory management throughout the association establishment process. The patch effectively closes this security gap by implementing proper input validation controls that align with industry best practices for protocol implementation security and follows established standards for network protocol robustness as defined in various cybersecurity frameworks including those related to secure coding practices and defensive programming techniques.