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CVE-2026-72253
netfilter: nf_conntrack_sip: validate skb_dst() before accessing it
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-2026-72253 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 | fixed | 6.12.101-1 | Update the kernel and reboot. Fixed in 6.12.101-1. A running kernel keeps the old code until the machine restarts. |
| 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. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4745-1 · 2026-08-18 · text | 6.12.101-1~deb12u1 | Update the kernel and reboot. DLA-4745-1 shipped the fix on 2026-08-18, in 6.12.101-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
tc ingress and openvswitch do not guarantee routing information to be available. These subsystems use the conntrack helper infrastructure, and the SIP helper relies on the skb_dst() to be present if sip_external_media is set to 1 (which is disabled by default as a module parameter). This effectively disables the sip_external_media toggle for these subsystems without resulting in a crash.
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/nf_conntrack_sip.c
- What this is
- NETFILTERMAINTAINERS section matched on net/netfilter/ · netfilter-devel@vger.kernel.org · Maintained
- Kernel module
- nf_conntrack_sip
Check it on the machine
grep -wE 'CONFIG_NETFILTER|CONFIG_NF_CONNTRACK_SIP' /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 nf_conntrack_sipPrints 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_NF_CONNTRACK_SIP
- 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
- 7.5 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
- 0.70%, higher than 52.1% 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 |
|---|---|---|
| 4.3 | 5.10.266 | 7866116a040b |
| 4.3 | 5.15.217 | c5ef7228be04 |
| 4.3 | 6.1.184 | 0aec339694a5 |
| 4.3 | 6.6.148 | e64a48c50a1f |
| 4.3 | 6.12.101 | c199ed687c00 |
| 4.3 | 6.18.42 | 09755dc62b02 |
| 4.3 | 7.1.5 | b843a96252f6 |
| 4.3 | 7.2 | e5e24a365a5e |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4777-1 | 2026-09-08 | bookworm 6.1.187-1 | tracker |
| DLA-4745-1 | 2026-08-18 | bookworm 6.12.101-1~deb12u1 | 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
- Remote attackers reach set_expected_rtp_rtcp() by sending crafted SIP/SDP (e.g., INVITE) through Open vSwitch or tc ingress ct(helper=sip) on internet-facing VoIP SBC/NFV gateways where packets are conntrack-processed before skb_dst routing metadata is attached.
- AC:LAttack complexity, low
- Once sip_external_media=1, sip_direct_media=0, and the SIP helper are configured on OVS/tc ingress, the attacker fully controls SIP/SDP contents to reach the skb_dst(skb)->dev dereference without races or conditions outside their control.
- PR:NPrivileges required, none
- Exploitation requires no privileges on the victim host; a remote SIP peer only needs to deliver malicious signaling to an already-configured OVS/tc SIP ALG with sip_external_media enabled, with no authentication or local access.
- UI:NUser interaction, none
- No victim user interaction is required; the kernel SIP helper parses attacker-supplied SIP/SDP during conntrack processing in softirq without any user action beyond normal automated packet handling.
- S:UScope, unchanged
- A NULL pointer dereference in nf_conntrack_sip causes a kernel oops/panic within the same kernel security domain on the gateway; it does not cross VM, IOMMU, or sandbox boundaries.
- C:NConfidentiality impact, none
- The failure is a direct NULL pointer dereference from skb_dst(skb) being NULL on tc/OVS ingress paths; there is no use-after-free, out-of-bounds read, or other memory disclosure primitive.
- I:NIntegrity impact, none
- Accessing skb_dst(skb)->dev when skb_dst is NULL cannot modify memory or hijack control flow beyond the immediate fault; CVSS guidance assigns None for pure NULL-deref crashes without write capability.
- A:HAvailability impact, high
- The invalid skb_dst dereference in set_expected_rtp_rtcp() during SIP SDP processing causes a kernel oops/panic-class fault, denying availability on the VoIP gateway until reboot; the crash is reliably reproducible with crafted SIP traffic.