Bug 2464467 (CVE-2026-31696)

Summary: CVE-2026-31696 kernel: rxrpc: Fix missing validation of ticket length in non-XDR key preparsing
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security <prodsec-ir-bot>
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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 rxrpc component. An unprivileged user can exploit this by providing an excessively large ticket length during key preparsing. This improper validation leads to an oversized token calculation when the key is subsequently read, triggering a system warning and potentially causing a Denial of Service (DoS).
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Description OSIDB Bzimport 2026-05-01 15:08:28 UTC 
In the Linux kernel, the following vulnerability has been resolved:

rxrpc: Fix missing validation of ticket length in non-XDR key preparsing

In rxrpc_preparse(), there are two paths for parsing key payloads: the
XDR path (for large payloads) and the non-XDR path (for payloads <= 28
bytes). While the XDR path (rxrpc_preparse_xdr_rxkad()) correctly
validates the ticket length against AFSTOKEN_RK_TIX_MAX, the non-XDR
path fails to do so.

This allows an unprivileged user to provide a very large ticket length.
When this key is later read via rxrpc_read(), the total
token size (toksize) calculation results in a value that exceeds
AFSTOKEN_LENGTH_MAX, triggering a WARN_ON().

[ 2001.302904] WARNING: CPU: 2 PID: 2108 at net/rxrpc/key.c:778 rxrpc_read+0x109/0x5c0 [rxrpc]

Fix this by adding a check in the non-XDR parsing path of rxrpc_preparse()
to ensure the ticket length does not exceed AFSTOKEN_RK_TIX_MAX,
bringing it into parity with the XDR parsing logic.
Comment 1 Keith Grant 2026-05-01 19:29:34 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050118-CVE-2026-31696-d2de@gregkh/T