Look up another CVE · open CVE-2026-52999 in the interactive tracker
CVE-2026-52999
netfilter: nfnetlink_osf: fix out-of-bounds read on option matching
Published 2026-06-24 (4 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-2026-52999 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-4665-1 · 2026-07-03 · text | 6.1.176-1 | Update the kernel and reboot. DLA-4665-1 shipped the fix on 2026-07-03, in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.10-1 | Update the kernel and reboot. Fixed in 7.0.10-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once and passed by reference to nf_osf_match_one() for each fingerprint checked. During TCP option parsing, nf_osf_match_one() advances the shared ctx->optp pointer. If a fingerprint perfectly matches, the function returns early without restoring ctx->optp to its initial state. If the user has configured NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint. However, because ctx->optp was not restored, the next call to nf_osf_match_one() starts parsing from the end of the options buffer. This causes subsequent matches to read garbage data and fail immediately, making it impossible to log more than one match or logging incorrect matches. Instead of using a shared ctx->optp pointer, pass the context as a constant pointer and use a local pointer (optp) for TCP option traversal. This makes nf_osf_match_one() strictly stateless from the caller's perspective, ensuring every fingerprint check starts at the correct option offset.
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/nfnetlink_osf.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nfnetlink_osf
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NETFILTER_NETLINK_OSF' /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 nfnetlink_osfPrints 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, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- Build switches
- CONFIG_NETFILTER, CONFIG_NETFILTER_NETLINK_OSF
- 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
- 2026-06-24 (4 months ago)source
- CVSS
- 9.1 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.59%, higher than 47.2% 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 |
|---|---|---|
| 5.0 | 5.10.258 | 0145548346c4 |
| 5.0 | 5.15.209 | 1c136f2c44a5 |
| 5.0 | 6.1.175 | 1e19a07291bb |
| 5.0 | 6.6.141 | 32e50f92c7cf |
| 5.0 | 6.12.91 | 70a3f31d25cf |
| 5.0 | 6.18.33 | 21883587593d |
| 5.0 | 7.0.10 | edb78a142d2e |
| 5.0 | 7.1 | f5ca450087c3 |
| 4.19.26 | 0 | 0 |
| 4.20.13 | 0 | 0 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4671-1 | 2026-07-05 | bullseye 6.1.176-1~deb11u1 | tracker |
| DLA-4665-1 | 2026-07-03 | bookworm 6.1.176-1 | tracker |
| DLA-4664-1 | 2026-07-03 | bullseye 5.10.259-1 | 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:NAttack vector, network
- The vulnerable matcher runs on received IPv4 TCP SYN packets in the OSF netfilter hook path once OSF matching is configured, including PRE_ROUTING, LOCAL_IN, and FORWARD. A remote peer can supply the TCP options that drive the vulnerable parsing.
- AC:LAttack complexity, low
- There is no race or hard-to-win timing condition; the attacker can craft and retry SYN packets with chosen TCP options. The need for OSF rules/fingerprints is part of the vulnerable deployment scenario.
- PR:NPrivileges required, none
- The packet-processing path has no attacker privilege or authentication check. CAP_NET_ADMIN checks apply to installing OSF state/rules, not to sending packets that trigger an already configured matcher.
- UI:NUser interaction, none
- No victim user action is needed after the vulnerable OSF configuration is present. Packets are processed automatically by the kernel receive path.
- S:UScope, unchanged
- The bug remains within the kernel/netfilter security authority. It does not cross a VM, IOMMU, or other separate security boundary.
- C:HConfidentiality impact, high
- The bug reads beyond the TCP options buffer or its stack copy during subsequent fingerprint checks after ctx->optp has been advanced. Because this is a kernel out-of-bounds read that can expose adjacent kernel memory through matching/logging side effects, confidentiality is High under the required conservative rule.
- I:NIntegrity impact, none
- The flaw is an out-of-bounds read and does not provide a write primitive or direct data modification. Incorrect OSF matches/log entries do not amount to modification of protected system data.
- A:HAvailability impact, high
- The out-of-bounds read occurs in the kernel packet path and can be triggered repeatedly by crafted packets. On hardened/debug builds or unfavorable boundary placement it can produce an oops/panic, so availability is scored High conservatively.