CVE-2026-31719
Published: 01 May 2026
Summary
CVE-2026-31719 is a high-severity an unspecified weakness vulnerability in Linux Linux Kernel. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Steal or Forge Kerberos Tickets (T1558); ranked at the 12.0th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified are NIST 800-53 SI-2 (Flaw Remediation) and SC-13 (Cryptographic Protection).
Deeper analysis
CVE-2026-31719 affects the Linux kernel's krb5enc cryptographic module, which handles Kerberos 5 encryption and decryption. The vulnerability arises in krb5enc_dispatch_decrypt(), where the skcipher completion callback is incorrectly set to the caller's own handler. This causes asynchronous decryption to signal completion to the caller without invoking krb5enc_dispatch_decrypt_hash(), thereby skipping the integrity verification via hash check. The encrypt path avoids this issue by using an intermediate callback, krb5enc_encrypt_done, to chain into hash computation.
A network-based attacker requires no privileges or user interaction and faces low attack complexity, per the CVSS 3.1 score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N). Exploitation enables high integrity impact by bypassing hash verification during async decryption, potentially allowing acceptance of tampered Kerberos-encrypted data. Additional fixes address improper EBUSY/EINPROGRESS handling and unset MAY_BACKLOG on async paths to prevent misleading notifications.
Mitigation involves applying patches from the Linux kernel stable repository, available via commits 07cbb1bd424370671814a862913c99a6e1441588, 3bfbf5f0a99c991769ec562721285df7ab69240b, and e51f42114abbdf47f29dda43e7826be28907fcd2. These introduce krb5enc_decrypt_done as an intermediate callback to ensure hash verification on async skcipher completion, matching the encrypt path, while correcting request completion and backlog signaling.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-26528
Vulnerability details
In the Linux kernel, the following vulnerability has been resolved: crypto: krb5enc - fix async decrypt skipping hash verification krb5enc_dispatch_decrypt() sets req->base.complete as the skcipher callback, which is the caller's own completion handler. When the skcipher completes asynchronously, this signals…
more
"done" to the caller without executing krb5enc_dispatch_decrypt_hash(), completely bypassing the integrity verification (hash check). Compare with the encrypt path which correctly uses krb5enc_encrypt_done as an intermediate callback to chain into the hash computation on async completion. Fix by adding krb5enc_decrypt_done as an intermediate callback that chains into krb5enc_dispatch_decrypt_hash() upon async skcipher completion, matching the encrypt path's callback pattern. Also fix EBUSY/EINPROGRESS handling throughout: remove krb5enc_request_complete() which incorrectly swallowed EINPROGRESS notifications that must be passed up to callers waiting on backlogged requests, and add missing EBUSY checks in krb5enc_encrypt_ahash_done for the dispatch_encrypt return value. Unset MAY_BACKLOG on the async completion path so the user won't see back-to-back EINPROGRESS notifications.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise TechniquesAI
Why these techniques?
Bypassing Kerberos hash verification on async decrypt directly enables forging/modifying tickets (T1558) and tampering with transmitted Kerberos data (T1565.002).
CVEs Like This One
Affected Assets
Mitigating Controls
Mitigating Controls (NIST 800-53 r5) AI
Timely patching of the Linux kernel flaw in krb5enc_dispatch_decrypt() directly remediates the async decryption hash verification bypass.
Requires FIPS-validated cryptographic mechanisms for integrity protection, addressing improper chaining in Kerberos decryption callbacks.
Enforces integrity verification of information using hashes, mitigating the skipped krb5enc_dispatch_decrypt_hash() during async operations.