Look up another CVE · open CVE-2026-43091 in the interactive tracker
CVE-2026-43091
xfrm: Wait for RCU readers during policy netns exit
Published 2026-05-06 (5 months ago) by the Linux kernel CNA. Subsystem net/xfrm. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-43091 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 | vulnerable | 6.1.190-1 | No fix published anywhere yet, neither in Debian nor upstream for the series bookworm tracks. Watch the Debian tracker page for this CVE. Advisories for bookworm have historically landed a median of 23 days after publication. |
| Debian 13trixie | fixed | 6.12.85-1 | Update the kernel and reboot. Fixed in 6.12.85-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.19.14-1 | Update the kernel and reboot. Fixed in 6.19.14-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.14-1 | Update the kernel and reboot. Fixed in 6.19.14-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
xfrm_policy_fini() frees the policy_bydst hash tables after flushing the policy work items and deleting all policies, but it does not wait for concurrent RCU readers to leave their read-side critical sections first. The policy_bydst tables are published via rcu_assign_pointer() and are looked up through rcu_dereference_check(), so netns teardown must also wait for an RCU grace period before freeing the table memory. Fix this by adding synchronize_rcu() before freeing the policy hash tables.
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/xfrm/xfrm_policy.c
- What this is
- NETWORKING [IPSEC]MAINTAINERS section matched on net/xfrm/ · netdev@vger.kernel.org · Maintained
Check it on the machine
grep -w CONFIG_XFRM /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 builds this code. Every release below compiles the affected file into the kernels it ships.
- bookworm, trixie, forky, sidy
- y
- built into the kernel image on every flavour - only a patch removes it
- Build switch
- CONFIG_XFRM
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
- 2026-05-06 (5 months ago)source
- CVSS
- 7.8 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.18%, higher than 6.5% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/xfrm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.9 | 6.6.136 | b66920a3348c |
| 4.9 | 6.12.83 | 438b1f668ad5 |
| 4.9 | 6.18.24 | 3733fce2871c |
| 4.9 | 6.19.14 | 33a3149dd81a |
| 4.9 | 7.0 | 069daad4f2ae |
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:LAttack vector, local
- The vulnerable path requires local control of a network namespace/XFRM policy state and concurrent namespace teardown; remote packets can exercise XFRM policy lookups, but a remote attacker cannot normally trigger the required netns exit.
- AC:LAttack complexity, low
- The race is attacker-controllable by creating XFRM policies, generating policy lookups, and tearing down the namespace concurrently; no rare configuration or victim-controlled timing is required beyond winning a repeatable local race.
- PR:LPrivileges required, low
- XFRM netlink operations require CAP_NET_ADMIN in the target network namespace, but an unprivileged local user can obtain that in a new user+network namespace on common userns-enabled systems.
- UI:NUser interaction, none
- No victim action is required once the local attacker can run code and issue the relevant namespace, netlink, and traffic operations.
- S:UScope, unchanged
- The impact is within the kernel security authority; this is a standard kernel memory-safety issue rather than a VM, IOMMU, or separate-scope escape.
- C:HConfidentiality impact, high
- This is a use-after-free of an RCU-published XFRM policy hash table, and stale readers may dereference reallocated attacker-influenced memory during policy lookup.
- I:HIntegrity impact, high
- As a kernel UAF in a list traversal path that can reach policy object handling, the freed memory can plausibly be shaped into fake list/policy data and leveraged for kernel memory corruption.
- A:HAvailability impact, high
- At minimum, dereferencing freed hash-table memory during packet or route policy lookup can trigger a kernel oops or panic, causing high availability impact.