CVE-2026-46193 xfrm: ah: account for ESN high bits in async callbacks
Incorrect memory offset handling in Linux kernel AH async callbacks with ESN causes packet loss and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-46193?
CVE-2026-46193 is a medium-severity vulnerability in Linux kernel, published on 28 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
xfrm: ah: account for ESN high bits in async callbacks
AH allocates its temporary auth/ICV layout differently when ESN is enabled: the async ahash setup appends a 4-byte seqhi slot before the ICV or auth_data area, but the async completion callbacks still reconstruct the temporary layout as if seqhi were absent.
With an async AH implementation selected, that makes AH copy or compare the wrong bytes on both the IPv4 and IPv6 paths. In UML repro on IPv4 AH with ESN and forced async hmac(sha1), ping fails with 100% packet loss, and the callback logs show the pre-fix drift:
ah4 output_done: esn=1 err=0 icv_off=20 expected_off=24 ah4 input_done: esn=1 auth_off=20 expected_auth_off=24 icv_off=32 expected_icv_off=36
Reconstruct the callback-side layout the same way the setup path built it by skipping the ESN seqhi slot before locating the saved auth_data or ICV. Per RFC 4302, the ESN high-order 32 bits participate in the AH ICV computation, so the async callbacks must account for the seqhi slot.
Post-fix, the same IPv4 AH+ESN+forced-async-hmac(sha1) UML repro shows the corrected offset (ah4 output_done: esn=1 err=0 icv_off=24 expected_off=24) and ping succeeds; net/ipv4/ah4.o and net/ipv6/ah6.o build clean at W=1. IPv6 AH+ESN was not exercised at runtime, and the change has not been tested against a real async hardware AH engine.
Which versions are affected by CVE-2026-46193?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-46193?
Apply the vendor's patch.
Is CVE-2026-46193 being exploited?
There is no known exploitation of CVE-2026-46193 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-88958, BELL-CVE-2026-46193, DEBIAN-CVE-2026-46193, GHSA-h5pr-w979-v38m, ROOT-OS-DEBIAN-11-CVE-2026-46193, ROOT-OS-DEBIAN-12-CVE-2026-46193 and 3 more.