Look up another CVE · open CVE-2026-74564 in the interactive tracker
CVE-2026-74564
netfilter: xt_hashlimit: validate hashtable supports XT_HASHLIMIT_RATE_MATCH
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem net/netfilter. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-74564 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 | fixedDLA-4777-1 · 2026-09-08 · text | 6.1.187-1 | Update the kernel and reboot. DLA-4777-1 shipped the fix on 2026-09-08, in 6.1.187-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixedDSA-6466-1 · 2026-08-25 · text | 6.12.105-1 | Update the kernel and reboot. DSA-6466-1 shipped the fix on 2026-08-25, in 6.12.105-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.8-1 | Update the kernel and reboot. Fixed in 7.1.8-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4788-1 · 2026-09-19 · text | 6.12.107-1~deb12u1 | Update the kernel and reboot. DLA-4788-1 shipped the fix on 2026-09-19, in 6.12.107-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
The XT_HASHLIMIT_RATE_MATCH flag mode changes the semantics of the dsthash_ent structure which represents an entry in the hashtable. There is a union area which uses a different layout to express the rate match mode. Update .checkentry path to validate the XT_HASHLIMIT_RATE_MATCH mode flag is requested by two or more different rules that refer to the same hashtable. Otherwise, uninitialized access to the burst field in the union is possible. Reject the use of the XT_HASHLIMIT_RATE_MATCH mode flag if set on by revision less than 3 too.
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/netfilter/xt_hashlimit.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- xt_hashlimit
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NETFILTER_XT_MATCH_HASHLIMIT' /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 xt_hashlimitPrints 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 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.
- bookworm, trixie, forky, sid, bookworm · linux-6.12m
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NETFILTER_XT_MATCH_HASHLIMIT
- 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
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:Nsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.12%, higher than 1.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/netfilter
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.14 | 5.10.265 | 402befce5854 |
| 4.14 | 5.15.216 | dee686b5e7f2 |
| 4.14 | 6.1.183 | f76ab783e7d8 |
| 4.14 | 6.6.151 | 24683fea1f06 |
| 4.14 | 6.12.103 | 32ec8d4aba2c |
| 4.14 | 6.18.44 | d186f77d18bd |
| 4.14 | 7.1.8 | 06a76334243c |
| 4.14 | 7.2 | 305b63e14022 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4788-1 | 2026-09-19 | bookworm 6.12.107-1~deb12u1 | tracker |
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DSA-6466-1 | 2026-08-25 | trixie 6.12.105-1 | tracker |
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
- Exploitation requires installing conflicting xt_hashlimit iptables rules via the IPT_SO_SET_REPLACE netlink path (CAP_NET_ADMIN), which is local netfilter configuration per kernel CVSS guidance; the uninitialized burst read occurs later during packet matching in hashlimit_mt_common().
- AC:LAttack complexity, low
- An attacker with CAP_NET_ADMIN can deterministically install two rules sharing one hashtable name—one standard hashlimit and one with XT_HASHLIMIT_RATE_MATCH—so the first packet evaluated by both rules triggers uninitialized burst access without races or external timing.
- PR:LPrivileges required, low
- Installing iptables hashlimit rules requires CAP_NET_ADMIN, which unprivileged users can obtain in their own network namespace via user namespaces (unshare -Urn) on common Linux distributions, containers, and Kubernetes workloads with NET_ADMIN capability.
- UI:NUser interaction, none
- No victim interaction is required; once the conflicting hashlimit rules are installed, the attacker fully controls exploitation by sending network packets that traverse the affected iptables hooks (INPUT, FORWARD, PREROUTING).
- S:UScope, unchanged
- Impact is confined to kernel netfilter hashlimit state and packet-filtering decisions within the target network namespace; it does not cross a VM, container-to-host, or IOMMU security boundary.
- C:HConfidentiality impact, high
- The rate-match path reads an uninitialized burst field from kmem_cache-allocated dsthash_ent entries whose standard-mode initialization only writes the first 24 bytes of the rateinfo union, exposing stale kernel slab heap contents.
- I:HIntegrity impact, high
- Cross-mode union aliasing causes rate-match logic to read uninitialized burst and write current_rate/prev_window over credit/credit_cap/cost fields, corrupting shared hashtable entries and enabling arbitrary firewall match verdict manipulation (type confusion).
- A:NAvailability impact, none
- The vulnerability causes uninitialized memory reads and union field corruption affecting match results, but does not trigger kernel oops, panic, hang, or host-level denial of service; impact is incorrect packet classification rather than system crash.