Bug 2482000 (CVE-2026-46033)

Summary: CVE-2026-46033 kernel: crypto: authencesn - reject short ahash digests during instance creation
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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Priority: high    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's `authencesn` cryptographic module. This vulnerability arises from insufficient validation of cryptographic digest sizes during the creation of new instances. A local attacker could exploit this by providing a malformed input, leading to an out-of-bounds memory access. This could cause system instability, a denial of service (DoS), or potentially enable unauthorized access to sensitive information or system control.
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Description OSIDB Bzimport 2026-05-27 15:06:24 UTC 
In the Linux kernel, the following vulnerability has been resolved:

crypto: authencesn - reject short ahash digests during instance creation

authencesn requires either a zero authsize or an authsize of at least
4 bytes because the ESN encrypt/decrypt paths always move 4 bytes of
high-order sequence number data at the end of the authenticated data.

While crypto_authenc_esn_setauthsize() already rejects explicit
non-zero authsizes in the range 1..3, crypto_authenc_esn_create()
still copied auth->digestsize into inst->alg.maxauthsize without
validating it.  The AEAD core then initialized the tfm's default
authsize from that value.

As a result, selecting an ahash with digest size 1..3, such as
cbcmac(cipher_null), exposed authencesn instances whose default
authsize was invalid even though setauthsize() would have rejected the
same value.  AF_ALG could then trigger the ESN tail handling with a
too-short tag and hit an out-of-bounds access.

Reject authencesn instances whose ahash digest size is in the invalid
non-zero range 1..3 so that no tfm can inherit an unsupported default
authsize.
Comment 1 Keith Grant 2026-05-27 19:57:48 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026052749-CVE-2026-46033-dcad@gregkh/T