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CVE-2026-74750
ovpn: defer key slot crypto freeing to workqueue
Published 2026-08-26 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74750 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 | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.10-1 | Update the kernel and reboot. Fixed in 7.1.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Key slots are released through a kref and the existing release path frees the AEAD transforms from an RCU callback. That is not safe for all crypto implementations: crypto_free_aead can sleep, for example when an async or hardware implementation has teardown work to complete. Use queue_rcu_work for key-slot release. This keeps the RCU grace period needed by lockless key-slot readers, but runs the actual crypto teardown from workqueue context where sleeping is allowed. Once the rcu_work callback runs, pre-existing RCU readers are gone, and the final kref put already proves that no transform user remains, so the worker can release the AEAD transforms and free the slot directly. The previous patch drains ovpn_wq during module exit, so queued key-slot teardown work cannot outlive module text.
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.
drivers/net/ovpn/crypto.c
drivers/net/ovpn/crypto.h
drivers/net/ovpn/crypto_aead.c
drivers/net/ovpn/crypto_aead.h
- What this is
- OPENVPN DATA CHANNEL OFFLOADMAINTAINERS section matched on drivers/net/ovpn/ · openvpn-devel@lists.sourceforge.net · Supported
- Kernel module
- ovpn
Check it on the machine
grep -w CONFIG_OVPN /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.
lsmod | grep -w ovpnPrints a line if that module is loaded right now, and nothing if it is not. One that is not loaded can still be loaded later by anything that needs it.
Show whether Debian builds this, per release
Debian builds this as a loadable module. Every release with an answer below compiles it as a module on every flavour, so whether the code is in the running kernel depends on whether that module is loaded. The build rule could not be established for 2 releases, so nothing is claimed about those.
- bookworm, trixie?
- forky, sidm
- ?
- not established - no Makefile entry for the affected file
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
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 switch
- CONFIG_OVPN
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
- 2026-08-26 (2 months ago)source
- CVSS
- 7.5 high
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.61%, higher than 48.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.16 | 6.18.57 | 5cea36555944 |
| 6.16 | 7.1.10 | 0f77ed5ee919 |
| 6.16 | 7.2 | 2da3dfa1ddfe |
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
- Key-slot teardown runs from peer removal paths reachable over the network: remote TCP RST/FIN closes ovpn_tcp_close() and keepalive expiry deletes silent VPN peers, both releasing crypto key slots whose RCU callbacks call crypto_free_aead().
- AC:LAttack complexity, low
- Once an ovpn instance with peers/keys exists, a remote party can deterministically trigger teardown (silence until keepalive timeout or force TCP disconnect) without winning races or influencing memory layout; async/hardware AEAD drivers make the sleeping-in-RCU callback reliably observable.
- PR:NPrivileges required, none
- Exploitation needs only network reachability to an operational OpenVPN offload tunnel (or ability to reset its transport); no local account, CAP_NET_ADMIN, or init-namespace root on the victim is required beyond normal VPN service deployment.
- UI:NUser interaction, none
- No victim user action is required after ovpn is configured; peer teardown and key-slot release are driven automatically by transport disconnect or configured keepalive expiry from remote peer behavior.
- S:UScope, unchanged
- Impact is confined to kernel networking/crypto teardown on the same host; it does not cross VM, container, or IOMMU security boundaries and is standard in-kernel denial-of-service, not privilege escalation across authorities.
- C:NConfidentiality impact, none
- The bug is calling a potentially sleeping crypto_free_aead() from an RCU callback, not an out-of-bounds read, UAF, or disclosure primitive; teardown occurs only after RCU grace period and final kref put with no attacker-readable side channel.
- I:NIntegrity impact, none
- Sleeping during AEAD transform release does not grant attacker-controlled memory writes or code execution; it violates atomic-context rules and can destabilize the kernel but does not corrupt adjacent structures into exploitable write primitives.
- A:HAvailability impact, high
- crypto_free_aead() may block on async/hardware teardown while running in an RCU callback, triggering BUG: sleeping function called from invalid context, RCU stall, oops, or kernel panic and enabling repeatable remote denial of service against internet-facing VPN gateways.