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CVE-2026-72098
dm-verity: fix buffer overflow in FEC calculation
Published 2026-08-15 (2 months ago) by the Linux kernel CNA. Subsystem drivers/md. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-72098 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 | vulnerable | 6.12.113-1 | No fix published anywhere yet, neither in Debian nor upstream for the series trixie tracks. Watch the Debian tracker page for this CVE. Advisories for trixie have historically landed a median of 11 days after publication. |
| 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
There's a buffer overflow in dm-verity-fec: if (neras && *neras <= v->fec->roots) fio->erasures[(*neras)++] = i; This allows *neras to reach roots + 1 (the post-increment pushes it past roots). This value is then passed as no_eras to decode_rs8(). Inside the RS decoder (lib/reed_solomon/decode_rs.c:113-121), the erasure locator polynomial loop writes lambda[j] where j can reach nroots + 1 — one element past the end of lambda[] (which is sized nroots + 1, valid indices 0..nroots). The out-of-bounds write lands on syn[0], corrupting the syndrome buffer.
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/md/dm-verity-fec.c
drivers/md/dm-verity-fec.h
- What this is
- DEVICE-MAPPER (LVM)MAINTAINERS section matched on drivers/md/dm* · dm-devel@lists.linux.dev · Maintained
- Kernel module
- dm_verity
Check it on the machine
grep -wE 'CONFIG_DM_VERITY|CONFIG_DM_VERITY_FEC|CONFIG_MD' /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 dm_verityPrints 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_DM_VERITY, CONFIG_DM_VERITY_FEC, CONFIG_MD
- 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
- 9.8 critical
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:Hsource recompute it - Attack vector
- network (AV:N)source
- EPSS
- 0.66%, higher than 50.8% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/md
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.5 | 6.18.42 | 5488d3a69d20 |
| 4.5 | 7.1.5 | f7990c2b0f08 |
| 4.5 | 7.2 | 31d6e6c0ba8d |
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
- In cloud/network-boot deployments where dm-verity data, hash, or FEC backing devices are served over NBD/iSCSI/TCP, a remote block provider can supply crafted blocks that drive the FEC erasure-correction path during ordinary read I/O through verity_map without local code execution.
- AC:LAttack complexity, low
- A crafted backing image or malicious network-block responses can deterministically produce at least fec_roots+1 hash-mismatched or failed message blocks in one RS group, reliably reaching the off-by-one no_eras path on the second FEC decode attempt after verification failure.
- PR:NPrivileges required, none
- Triggering requires only read I/O against an active dm-verity+FEC mapping; a remote NBD/iSCSI peer needs no account or privileges on the victim host, and unprivileged local processes with read access to the mapped device or filesystem can also reach the vulnerable FEC path.
- UI:NUser interaction, none
- Exploitation is driven by automatic boot-time reads, udev probing, or ordinary filesystem I/O on the dm-verity device; no specific victim action beyond normal system operation is required once corruption is present.
- S:UScope, unchanged
- The overflow corrupts kernel heap Reed-Solomon scratch buffers during dm-verity verification within the same kernel security authority; it does not by itself cross VM, IOMMU, or sandbox boundaries.
- C:HConfidentiality impact, high
- The inflated no_eras value causes decode_rs8 to XOR-write one uint16 past lambda[] into syn[0], corrupting adjacent kernel decoder state; such heap out-of-bounds writes can be leveraged for arbitrary memory disclosure.
- I:HIntegrity impact, high
- The same out-of-bounds write in the erasure-locator loop corrupts syndrome buffers later used to modify decoded message bytes, providing a heap memory-corruption primitive that can enable arbitrary kernel writes or control-flow hijacking.
- A:HAvailability impact, high
- Corrupting Reed-Solomon decoder state during dm-verity verification can cause kernel oops, panics, or hung I/O on critical read-only partitions (notably Android/embedded systems with FEC enabled), denying availability of the device or entire system.