CVE-2026-31431: Urgent Linux Kernel Crypto Subsystem Patch Released for Resource Transfer Vulnerability
Linux Kernel contains an incorrect resource transfer between spheres vulnerability that could allow for privilege escalation.
FREQUENTLY ASKED
What is CVE-2026-31431 and why is it significant?
CVE-2026-31431 is a high-severity security vulnerability in the Linux Kernel crypto component, specifically algif_aead. It is classified under CWE-699 and CWE-669, involving incorrect resource transfer between spheres. With a CVSS score of 7.8 and reports of active exploitation, this flaw is significant because it could allow a local attacker to escalate privileges or cause total technical impact on the system.
Which versions of the Linux Kernel are affected by this vulnerability?
The vulnerability affects several Linux Kernel versions, including 4.14, 5.10.254, 5.15.204, 6.1.170, 6.6.137, 6.12.85, 6.18.22, 6.19.12, and 7.0. It also impacts specific git commit versions such as 72548b093ee38a6d4f2a19e6ef1948ae05c181f7. Administrators should verify their kernel release immediately to determine exposure.
Has a patch been released for CVE-2026-31431?
Yes, a patch has been released to resolve this vulnerability. The fix involves reverting the algif_aead component to operate out-of-place rather than in-place, which removes the complexity that caused the incorrect resource transfer. Patches and technical details can be found via the official Linux Kernel archives and vendor security mailing lists such as Openwall.
What is the remediation deadline and what does it mean for compliance?
The remediation deadline for CVE-2026-31431 is May 15, 2026. For organizations following CISA BOD 22-01 or similar regulatory frameworks, missing this deadline may result in non-compliance. This date serves as a critical window to apply updates to production environments before the risk of automated exploitation increases significantly.
How can I check if my Linux deployment is affected?
To check if your instance is affected, run the command 'uname -r' in your terminal to identify the running kernel version. Compare this version against the affected list (e.g., 6.1.170, 6.6.137, etc.). If your version matches or is an older sub-version of these releases, you are likely vulnerable and should apply the latest upstream stable patches immediately.
CVE-2026-31431 represents a significant security breakdown within the Linux Kernel's cryptographic framework. Specifically targeting the algif_aead component, this vulnerability allows for Incorrect Resource Transfer Between Spheres (CWE-669), leading to a potential total technical impact. With a CVSS score of 7.8 (High) and an SSVC status indicating active exploitation, this is not a theoretical risk but an active threat to Linux-based infrastructure. Organizations must prioritize remediation before the May 15, 2026 deadline to maintain compliance and secure their environments against local privilege escalation (LPE).
To understand CVE-2026-31431, one must look at the Linux Kernel's User-space Interface for AEAD (Authenticated Encryption with Associated Data) ciphers. The algif_aead module allows applications in user-space to request encryption or decryption services from the kernel's internal crypto API.
Understanding CWE-669: Incorrect Resource Transfer Between Spheres
The root of this vulnerability lies in CWE-669, which describes a failure to maintain strict boundaries when transferring resources—such as memory buffers or data objects—between different protection domains (spheres). In the context of the Linux Kernel, these spheres are the user-space and kernel-space. When algif_aead attempts to process data, it must handle memory pages mapped from user-space securely. If the kernel incorrectly assumes that the source and destination buffers reside in the same memory mapping or "sphere," it may perform operations that bypass intended access controls or corrupt kernel memory.
The Failure of In-Place Crypto Operations
The technical description reveals that this vulnerability was introduced by an optimization attempt. Kernel developers previously introduced "in-place" operations for algif_aead (commit 72548b093ee3). In-place operations mean that the encrypted data is written directly back into the same memory buffer where the plaintext originated. While this saves memory and increases performance, it is inherently dangerous if the source and destination come from different memory mappings.
In CVE-2026-31431, the kernel failed to account for cases where the associated data (AD) and the payload were mapped differently. By attempting to operate in-place under these conditions, the kernel encountered a logic error nicknamed "Copy-Fail." This error allowed for the manipulation of memory buffers across boundaries, potentially permitting a local user to overwrite sensitive kernel structures or read data they should not have access to. The fix effectively reverts algif_aead to "out-of-place" operations, sacrificing minor performance gains for the absolute necessity of memory safety.
Who Is Affected
This vulnerability impacts a wide range of Linux users, particularly those running modern distributions that utilize the AF_ALG socket interface for cryptographic tasks. Affected versions span from the long-term supported (LTS) 4.14 branch up to the latest 7.0 releases.
Compliance and BOD 22-01 Implications
Federal agencies and organizations adhering to CISA Binding Operational Directive (BOD) 22-01 must take note of the remediation deadline. Because the SSVC status is marked as active, the threat is considered imminent. Compliance necessitates that all affected systems be updated by May 15, 2026. Failure to apply these mitigations could leave organizations vulnerable to automated exploitation scripts that leverage the low attack complexity of this local exploit.
Official Remediation Steps
To mitigate the risk posed by CVE-2026-31431, administrators and security engineers should follow these steps:
Identify Current Kernel Version: Execute uname -r on all active Linux deployments to identify current versioning.
Cross-Reference Version List: If your kernel version is 4.14.x (earlier than the fix), 5.10.x, 5.15.x, 6.1.x, 6.6.x, 6.12.x, 6.18.x, 6.19.x, or 7.0, you are likely affected.
Apply Upstream Patches: Obtain the fix from the official Linux Kernel stable tree. The fix involves reverting the in-place operation logic in crypto/algif_aead.c. Reference the patch URL: http://www.openwall.com/lists/oss-security/2026/04/29/23.
Distro-Specific Updates: For users of Ubuntu, RHEL, Debian, or Fedora, use the standard package manager (e.g., sudo apt update && sudo apt upgrade) once the distribution maintainers have backported the fix to their respective repositories.
Verify Integrity: After rebooting into the new kernel, verify that the algif_aead module is no longer operating on the vulnerable logic by checking the kernel git logs for the inclusion of the revert commit.
Security Best Practices for Kernel Hardening
Beyond patching, the following defensive measures can reduce the attack surface for resource transfer vulnerabilities:
Restrict AF_ALG Sockets: If your applications do not require user-space access to kernel crypto, consider disabling or restricting the AF_ALG socket family via Linux Security Modules (LSMs) like AppArmor or SELinux.
Implement Least Privilege: Ensure that local users operate with minimal privileges. Since this is a local attack (AV:L), limiting shell access and using containers with reduced capabilities can disrupt the attack chain.
Monitor System Calls: Use tools like auditd to monitor suspicious calls to the socket interface, particularly those involving AEAD cipher requests from unauthorized binaries.
Enable Kernel Page Table Isolation (KPTI): While primarily a mitigation for side-channel attacks, KPTI strengthens the isolation between kernel and user spheres, adding a layer of defense against mapping-related flaws.
Regular Memory Auditing: Utilize KASAN (Kernel Address Sanitizer) in testing environments to detect improper memory access patterns before they reach production systems.
Maintain Immutable Infrastructure: In cloud environments, prefer replacing instances with patched images rather than patching in-place to ensure no remnants of a potentially compromised state persist.
By addressing CVE-2026-31431 immediately, organizations can close a critical gap in their Linux security posture and defend against an actively exploited vulnerability in one of the most sensitive areas of the OS: the cryptographic subsystem.