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CVE-2026-74433
rxrpc: Fix UAF in rxgk_issue_challenge()
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/rxrpc. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74433 in every release this site tracks, and what each one means in practice. Every status below is the one the Debian Security Team publishes for this CVE. source
| Release | Status | Version | What this means |
|---|---|---|---|
| Debian 12bookworm | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| Debian 14forky | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.5-1 | Update the kernel and reboot. Fixed in 7.1.5-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Fix rxgk_issue_challenge() to free the page containing the challenge content after invoking the tracepoint as the whdr passed to the tracepoint points into the page just freed.
Where it lives
The fix touches these files. If the subsystem is one you do not use, the practical exposure is lower, though the package is still the vulnerable one.
net/rxrpc/rxgk.c
- What this is
- RXRPC SOCKETS (AF_RXRPC)MAINTAINERS section matched on net/rxrpc/ · linux-afs@lists.infradead.org · Supported
Check it on the machine
grep -wE 'CONFIG_AF_RXRPC|CONFIG_RXGK' /boot/config-$(uname -r)Reads the booted kernel's own configuration, on the machine and nowhere else. =y is built in, =m is a module, and an is not set line means the code is not there.
Show whether Debian builds this, per release
Debian does not build this code in 2 releases. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidn
- ?
- not established - no Makefile entry for the affected file
- n
- not enabled on any flavour - this release does not build the code
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
- Build switches
- CONFIG_AF_RXRPC, CONFIG_RXGK
- Reads as
- all on means the file is compiled; any one off means it is not.
From the configuration Debian publishes for every kernel flavour it builds. It covers only the architectures Debian ships a linux-config package for, and nothing about a kernel you built yourself. Debian's own status above stays authoritative about the source package.MAINTAINERS kbuild Makefiles Debian linux-config packages
Signals
- Published
- 2026-08-15 (2 months ago)source
- CVSS
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.65%, higher than 50.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- net/rxrpc
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.40 | 844b8525ce50 |
| 6.16 | 7.1.5 | 83bb0ed050e2 |
| 6.16 | 7.2 | 107a4cb0d47e |
Why the CNA scored it this way
Quoted from the kernel CNA's own scoring file, word for word. A highlighted metric carries the most severe value CVSS v3.1 defines for it, which is what pushes the score up. source
- AV:NAttack vector, network
- The bug is in rxgk_issue_challenge() on the RxRPC server path reached when a remote UDP RxRPC DATA packet starts a new call; packets enter via rxrpc_encap_rcv() and the I/O thread, then conn_event processing issues an RxGK challenge during the pre-auth handshake on internet-facing AFS/RxGK servers.
- AC:LAttack complexity, low
- Once an RxGK-enabled AFS kernel server is reachable, an attacker can reliably trigger rxgk_issue_challenge() by sending a valid incoming DATA packet with security index YFS-RxGK; the UAF is deterministic on each successful challenge transmission and does not depend on winning a race.
- PR:NPrivileges required, none
- The vulnerable code runs during initial server-side connection setup before client credentials are verified: an unauthenticated remote peer that can reach the RxRPC UDP port can force challenge issuance without any local account, capability, or namespace privilege on the target.
- UI:NUser interaction, none
- Exploitation requires only network packets to the RxRPC listener; no victim user action such as opening files, mounting AFS, or enabling tracing is needed for the server to automatically enter the challenging path and hit the bug.
- S:UScope, unchanged
- Impact is confined to kernel memory integrity and availability on the AFS/RxRPC server host; it does not by itself cross a VM, container, or IOMMU security boundary, though it may enable local privilege escalation on that host.
- C:HConfidentiality impact, high
- This is a use-after-free: __free_page() releases the challenge buffer before trace_rxrpc_tx_packet() dereferences whdr pointing into that page, enabling reads of freed slab/page memory and potential disclosure of kernel heap contents exploitable for KASLR bypass.
- I:HIntegrity impact, high
- UAF on the challenge transmit path can be leveraged with heap grooming to obtain controlled reuse of the freed page and build arbitrary kernel write or control-flow hijack primitives, not merely a bounded protocol corruption.
- A:HAvailability impact, high
- Reading or reusing freed kernel pages during challenge handling can provoke kernel oops/panic or wedged RxRPC/AFS service state; repeated remote triggering of the handshake can deny availability of the file service even without full exploitation.