CVE-2026-64439 crypto: krb5 - filter out async aead implementations at alloc

What is CVE-2026-64439?

CVE-2026-64439 is a critical use after free vulnerability in Linux kernel, published on 25 Jul 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

crypto: krb5 - filter out async aead implementations at alloc

krb5_aead_encrypt(), krb5_aead_decrypt() in rfc3961_simplified.c and rfc8009_encrypt(), rfc8009_decrypt() in rfc8009_aes2.c set a NULL completion callback and treat any negative return from crypto_aead_{encrypt,decrypt}() as terminal, falling through to kfree_sensitive(buffer). When the encrypt_name resolves to an async AEAD instance the request returns -EINPROGRESS, the buffer is freed while the backend's worker still holds a pointer, and the worker dereferences the freed slab on completion.

KASAN report under UML+SLUB with a synthetic async aead backend bound to krb5->encrypt_name:

BUG: KASAN: slab-use-after-free in t5_stub_complete+0x7d/0xc7

The helpers were written synchronously, so filter the async instances out at allocation time instead of plumbing crypto_wait_req() through every call site.

Reachable via net/rxrpc/rxgk.c, fs/afs/cm_security.c and net/ceph/crypto.c on systems with an async AEAD provider bound to the krb5 enctype name.

Weakness: CWE-416

Which versions are affected by CVE-2026-64439?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-64439?

Apply the vendor's patch.

Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.

Is CVE-2026-64439 being exploited?

There is no known exploitation of CVE-2026-64439 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as BELL-CVE-2026-64439, DEBIAN-CVE-2026-64439, GHSA-f86v-42xw-q4vj, ROOT-OS-UBUNTU-2204-CVE-2026-64439, UBUNTU-CVE-2026-64439.