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CVE-2026-72029
net: wwan: iosm: bound device offsets in the MUX downlink decoder
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/net. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72029 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 | fixed | 6.1.180-1 | Update the kernel and reboot. Fixed in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.100-1 | Update the kernel and reboot. Fixed in 6.12.100-1. 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. |
The vulnerability
What the bug is
mux_dl_adb_decode() walks a chain of aggregated datagram tables using offsets and lengths taken from the modem. first_table_index, next_table_index, table_length, datagram_index and datagram_length are all device supplied le values. Only first_table_index was checked, and only for being non zero. The decoder then formed adth = block + adth_index and read the table header and the datagram entries with no bound against the received skb. A modem that reports an index or a length past the downlink buffer makes the decoder read out of bounds. The buffer is IPC_MEM_MAX_DL_MUX_LITE_BUF_SIZE and skb->len is at most that, so skb->len is the real limit, but none of these in band offsets were checked against it. The table chain is also followed with no forward progress check. The loop takes the next table from adth->next_table_index and stops only when that reaches zero. A modem can stage two tables that point at each other, so the loop never ends. It runs in softirq and clones the skb on every pass. Validate every device offset and length against skb->len before use. The block header must fit. Each table header, on entry and after every next_table_index, must lie inside the skb. The datagram table must fit. Each datagram index and length must stay inside the skb. The header padding must not exceed the datagram length so the receive length does not wrap. Require each next_table_index to move forward so the chain cannot cycle. This was reproduced under KASAN as a slab out of bounds read on a normal downlink receive once the iosm net device is up.
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.
drivers/net/wwan/iosm/iosm_ipc_mux_codec.c
- What this is
- INTEL WWAN IOSM DRIVERMAINTAINERS section matched on drivers/net/wwan/iosm/ · netdev@vger.kernel.org · Orphan
- Kernel module
- iosm
Check it on the machine
grep -wE 'CONFIG_IOSM|CONFIG_WWAN' /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 iosmPrints 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, but not on every flavour. At least one release below builds the code on some of its kernel flavours and not on others, so the answer depends on the architecture and flavour installed.
- bookwormm
- trixieMnot built on armel/rpi
- forky, sidm
- m
- a loadable module on every flavour - check lsmod, can be blacklisted
- M
- a module where it is built at all; some flavours do not build it
- Build switches
- CONFIG_IOSM, CONFIG_WWAN
- 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
- 8.8 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.40%, higher than 32.4% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/net
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.18 | 6.1.178 | 155851e501d6 |
| 5.18 | 6.6.145 | 2b822df8e498 |
| 5.18 | 6.12.97 | 55cfea8e8d91 |
| 5.18 | 6.18.40 | 07f5eb6d268a |
| 5.18 | 7.1.5 | 77f0023f22f6 |
| 5.18 | 7.2 | 526b8ef54668 |
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:AAttack vector, adjacent network
- The vulnerable MUX decoder processes PCIe IPC downlink buffers from an adjacent Intel M.2 WWAN modem; a remote cellular/baseband attacker who compromises modem firmware can deliver malicious frames without local host access, analogous to Bluetooth/WiFi adjacent-radio threat models.
- AC:LAttack complexity, low
- The modem fully controls in-band offsets and lengths; the bug was reproduced as a KASAN slab OOB read on a normal downlink receive once the iosm netdev is up, requiring no races, special heap layout, or non-default kernel tuning beyond the IOSM driver and hardware.
- PR:NPrivileges required, none
- Exploitation requires no privileges on the victim host; downlink IPC is accepted autonomously from the modem via MSI/tasklet processing, and unprivileged users or user namespaces cannot inject data into this decoder path.
- UI:NUser interaction, none
- No victim action is needed beyond normal WWAN operation; on M.2-equipped systems the iosm interface is often brought up automatically, after which malicious modem-supplied downlink buffers are decoded without further user interaction.
- S:UScope, unchanged
- Impact is confined to host kernel memory and networking within the same OS security authority; this is standard kernel driver memory corruption, not a VM escape or cross-authority sandbox bypass.
- C:HConfidentiality impact, high
- Unvalidated device indices enable slab out-of-bounds reads of kernel heap memory; crafted offsets passed to ipc_mux_net_receive() can skb_pull/clone beyond the skb boundary and leak adjacent kernel data onto the wwan netdev via netif_rx.
- I:HIntegrity impact, high
- Attacker-controlled datagram indices and lengths feed skb_pull() and skb_trim() without skb bounds checks, and unchecked header padding can wrap receive lengths, enabling heap-adjacent corruption exploitable for arbitrary code execution.
- A:HAvailability impact, high
- Out-of-bounds reads can trigger kernel oops or panic, and cyclic next_table_index chains cause an unbounded tasklet loop that skb_clones on every pass, exhausting memory and freezing or crashing the system.