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CVE-2026-31675
net/sched: sch_netem: fix out-of-bounds access in packet corruption
Published 2026-04-25 (6 months ago) by the Linux kernel CNA. Subsystem net/sched. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-31675 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 | fixedDSA-6238-1 · 2026-04-30 · text | 6.12.85-1 | Update the kernel and reboot. DSA-6238-1 shipped the fix on 2026-04-30, in 6.12.85-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.19.12-1 | Update the kernel and reboot. Fixed in 6.19.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.19.12-1 | Update the kernel and reboot. Fixed in 6.19.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
In netem_enqueue(), the packet corruption logic uses get_random_u32_below(skb_headlen(skb)) to select an index for modifying skb->data. When an AF_PACKET TX_RING sends fully non-linear packets over an IPIP tunnel, skb_headlen(skb) evaluates to 0. Passing 0 to get_random_u32_below() takes the variable-ceil slow path which returns an unconstrained 32-bit random integer. Using this unconstrained value as an offset into skb->data results in an out-of-bounds memory access. Fix this by verifying skb_headlen(skb) is non-zero before attempting to corrupt the linear data area. Fully non-linear packets will silently bypass the corruption logic.
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/sched/sch_netem.c
- What this is
- NETEM NETWORK EMULATORMAINTAINERS section matched on net/sched/sch_netem.c · netdev@vger.kernel.org · Maintained
- Kernel module
- sch_netem
Check it on the machine
grep -w CONFIG_NET_SCH_NETEM /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 sch_netemPrints 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 switch
- CONFIG_NET_SCH_NETEM
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
- 2026-04-25 (6 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 7.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- net/sched
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.16 | 6.6.134 | a14b56863348 |
| 2.6.16 | 6.12.81 | 13a66ca1e235 |
| 2.6.16 | 6.18.22 | 3a2999704ac3 |
| 2.6.16 | 6.19.12 | 4fd258e281fa |
| 2.6.16 | 7.0 | d64cb81dcbd5 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DSA-6238-1 | 2026-04-30 | trixie 6.12.85-1 | 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
- Triggering requires local kernel interfaces: configuring a `netem` qdisc via rtnetlink and sending crafted AF_PACKET TX_RING traffic over an IPIP tunnel. This is not directly reachable by unauthenticated remote packets.
- AC:LAttack complexity, low
- The attacker controls the qdisc corruption setting and the fully non-linear skb construction path, with no race or victim state required. The corrupt probability can be configured to make the vulnerable access occur reliably.
- PR:LPrivileges required, low
- The path requires `CAP_NET_ADMIN` for traffic control and `CAP_NET_RAW` for AF_PACKET, but both are obtainable inside attacker-created user/network namespaces on systems permitting unprivileged user namespaces. Therefore this is low privilege rather than real init-namespace root.
- UI:NUser interaction, none
- No victim action is needed once the local attacker can issue the relevant netlink and socket syscalls. The attacker triggers the enqueue path directly.
- S:UScope, unchanged
- The corruption occurs within the kernel networking/qdisc subsystem and impacts the same kernel security authority. It is a standard local kernel compromise scenario, not a VM or hardware boundary escape.
- C:HConfidentiality impact, high
- The bug is an out-of-bounds kernel memory read-modify-write through an unconstrained offset from `skb->data`. As kernel memory corruption, successful exploitation can plausibly yield arbitrary kernel memory disclosure.
- I:HIntegrity impact, high
- The vulnerable operation flips a bit at an out-of-bounds kernel address, giving a kernel memory corruption primitive. Under the required overestimation rule, this supports potential control-flow hijack or privilege escalation.
- A:HAvailability impact, high
- The unconstrained out-of-bounds kernel access can fault or corrupt critical kernel memory. A local attacker can repeatedly trigger it, making kernel oops/panic or system instability high impact.