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CVE-2026-74344
bpf: Clear rb node linkage when freeing bpf_rb_root
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem kernel/bpf. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74344 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| 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
bpf_rb_root_free() detaches the root by copying the current rb_root_cached and then replacing the live root with RB_ROOT_CACHED. It then walks the copied root and drops each object contained in the tree. This leaves the rb node state intact while dropping the object. If the object is refcounted and survives the drop, its bpf_rb_node_kern still contains an owner pointer to the freed root and stale rb tree linkage. If a later bpf_rb_root allocation reuses the same address, bpf_rbtree_remove() can incorrectly pass the owner check and call rb_erase_cached() on a node whose rb pointers belong to the old tree. Mirror the list draining behavior by marking nodes as busy while the root is being detached, then clear the rb node and release the owner before dropping the containing object. This makes surviving nodes unowned and safe to reject from remove or accept for a later add.
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.
kernel/bpf/helpers.c
- What this is
- BPF [GENERAL] (Safe Dynamic Programs and Tools)MAINTAINERS section matched on kernel/bpf/ · bpf@vger.kernel.org · Supported
Check it on the machine
grep -wE 'CONFIG_BPF|CONFIG_BPF_SYSCALL' /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 switches
- CONFIG_BPF, CONFIG_BPF_SYSCALL
- 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
- 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
- 0.17%, higher than 6.3% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- kernel/bpf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.3 | 6.18.40 | 2eb39de4962f |
| 6.3 | 7.1.5 | 574612793bed |
| 6.3 | 7.2 | 4a7910ee060d |
| 6.2.15 | 0 | 0 |
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 bug is reached only through BPF kfuncs (bpf_rbtree_remove) and bpf_rb_root_free during BPF map/object teardown, all gated by the bpf(2) syscall and local BPF program loading; there is no network, adjacent-radio, or physical-device entry path.
- AC:LAttack complexity, low
- An attacker fully controls refcount retention (bpf_refcount_acquire), when bpf_rb_root_free runs (map close/delete or bpf_obj_drop), and subsequent bpf_rb_root reallocation to reuse the freed address; no victim timing or uncontrollable heap layout is required beyond normal BPF allocator reuse.
- PR:LPrivileges required, low
- Exploitation requires loading BPF programs/maps using bpf_rb_root and refcounted graph nodes, which the kernel enforces with CAP_BPF at map BTF setup; on typical hosts this is reachable by an unprivileged user via user namespaces (CAP_BPF inside the namespace), not init-namespace root only.
- UI:NUser interaction, none
- No action by another user or administrator is required; the attacker loads their own BPF program, populates the rbtree, triggers teardown, and calls bpf_rbtree_remove on stale nodes.
- S:UScope, unchanged
- Impact is kernel heap corruption and local privilege escalation within the same kernel security boundary; it is not a VM escape, IOMMU bypass, or cross-authority sandbox breakout.
- C:HConfidentiality impact, high
- Stale bpf_rb_node linkage lets bpf_rbtree_remove pass the owner check and invoke rb_erase_cached on bogus rb_left/rb_right/parent pointers, corrupting adjacent kernel memory in ways that can be turned into arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- rb_erase_cached on nodes whose rb pointers still reference a detached tree rewrites arbitrary kernel rbtree/list metadata and enables heap grooming for control-flow hijack and local root, not merely a bounded or transient modification.
- A:HAvailability impact, high
- Calling rb_erase_cached with inconsistent rb pointers commonly causes kernel BUG/oops/panic or wedged allocator state, giving reliable system crash or hang even before full exploitation.