CVE-2026-74752 in Linux
Summary
by MITRE • 08/26/2026
In the Linux kernel, the following vulnerability has been resolved:
sctp: validate cookie AUTH state before use
When cookie authentication is disabled, COOKIE_ECHO restores fixed-size AUTH fields directly from peer-controlled cookie bytes. A forged RANDOM length, HMAC list, or CHUNKS list can then reach association consumers with lengths or identifiers that were never validated against the local backing arrays.
A forged RANDOM length can cause out-of-bounds reads during key-vector construction. A forged HMAC identifier also caused a 32-byte write past a zero-length AUTH chunk, providing a primitive for a local privilege escalation chain.
Validate the cookie's RANDOM, HMACS, and CHUNKS parameters at the cookie trust boundary before copying them into the association. Reject invalid types, malformed lengths, unsupported HMAC identifiers, HMAC lists without SHA1, and forbidden chunk ids.
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Analysis
by VulDB Data Team • 08/26/2026
The Linux kernel Secure Transport Protocol (sctp) implementation contains a critical validation flaw within its cookie authentication mechanism that allows for out-of-bounds memory access and potential local privilege escalation. This vulnerability arises from the handling of COOKIE_ECHO chunks when cookie authentication is disabled on the receiving end. In this specific configuration, the kernel restores fixed-size AUTH fields directly from peer-controlled cookie bytes without performing sufficient integrity checks against locally configured security parameters. The core issue lies in the lack of validation for critical components such as RANDOM lengths, HMAC lists, and CHUNKS lists before they are processed or copied into the association state. This oversight creates a trust boundary violation where untrusted data from the network is treated with excessive confidence by the kernel's internal structures.
The technical consequences of this flaw are severe due to the direct manipulation of memory buffers during key-vector construction and chunk processing. Specifically, an attacker can craft a malicious COOKIE_ECHO message containing a forged RANDOM length field. When the kernel processes this malformed data, it attempts to construct cryptographic keys based on the provided length without verifying if that length is within acceptable bounds for the underlying arrays. This leads to out-of-bounds reads, allowing an attacker to potentially leak sensitive kernel memory contents or cause a denial of service through a kernel panic. Furthermore, the vulnerability extends beyond read operations; forged HMAC identifiers can trigger a thirty-two-byte write past a zero-length AUTH chunk boundary. This buffer overflow condition provides a powerful primitive for local privilege escalation, as it allows an unprivileged user to overwrite adjacent kernel memory structures with controlled data.
From a classification perspective, this vulnerability aligns with CWE-125 Out-of-bounds Read and CWE-787 Out-of-bounds Write, reflecting the fundamental memory safety errors exploited by the attack vector. The exploitation path involves manipulating protocol state through crafted network packets to bypass security controls, which maps closely to MITRE ATT&CK techniques related to input validation failures and potentially buffer overflow exploits for privilege escalation. The flaw highlights a common pitfall in kernel networking stacks where performance optimizations or simplified code paths inadvertently skip necessary sanity checks when specific features like cookie authentication are disabled.
To mitigate this vulnerability, the Linux kernel has been updated to enforce strict validation of cookie parameters at the trust boundary before they are copied into the association structure. The fix requires rejecting invalid types and malformed lengths for RANDOM fields. It also mandates that HMAC lists must contain supported identifiers, specifically requiring SHA1 support as per protocol standards, and forbids chunk IDs that are not permitted in this context. System administrators should ensure their systems are patched with the latest kernel updates to close these gaps. Additionally, while disabling cookie authentication might seem like a performance optimization, it exposes the system to these specific memory corruption risks; therefore, maintaining robust input validation regardless of feature toggles is essential for secure network stack operation.