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CVE-2026-80631
btrfs: lzo: reject compressed segment that overflows the compressed input
Published 2026-08-28 (2 months ago) by the Linux kernel CNA. Subsystem fs/btrfs. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-80631 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
lzo_decompress_bio() validates each on-disk segment length seg_len only against the workspace cbuf size, not against the compressed input size (compressed_len, the total folio bytes of the bio). A crafted extent can carry a segment whose seg_len passes the cbuf check but runs past the end of the bio, so copy_compressed_segment() walks off the last folio: get_current_folio() then returns the NULL folio from bio_next_folio(), and with CONFIG_BTRFS_ASSERT disabled (default) folio_size(NULL) faults. BUG: KASAN: null-ptr-deref in lzo_decompress_bio (fs/btrfs/lzo.c:383) Read of size 8 at addr 0000000000000000 by task kworker/u8:1/29 Workqueue: btrfs-endio simple_end_io_work kasan_report (mm/kasan/report.c:590) lzo_decompress_bio (fs/btrfs/lzo.c:383) end_bbio_compressed_read (fs/btrfs/compression.c:1065) btrfs_bio_end_io (fs/btrfs/bio.c:135) btrfs_check_read_bio (fs/btrfs/bio.c:180 fs/btrfs/bio.c:285) simple_end_io_work process_one_work worker_thread Reject any segment whose payload would extend beyond compressed_len before copying it, treating it as corruption like the other on-disk validation failures in this function.
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.
fs/btrfs/lzo.c
- What this is
- BTRFS FILE SYSTEMMAINTAINERS section matched on fs/btrfs/ · linux-btrfs@vger.kernel.org · Maintained
- Kernel module
- btrfs
Check it on the machine
grep -w CONFIG_BTRFS_FS /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 btrfsPrints 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_BTRFS_FS
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
- 2026-08-28 (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
- 0.61%, higher than 48.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/btrfs
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 5.15 | 6.18.57 | be7fb59512ff |
| 5.15 | 7.1.5 | 1641d058adfb |
| 5.15 | 7.2 | b0d27d43791b |
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
- On btrfs-backed NAS/cloud storage exported via nfsd or ksmbd, a remote client's read I/O is served by the server kernel through btrfs_do_readpage→btrfs_submit_compressed_read→lzo_decompress_bio, reaching the vulnerable LZO segment parser without local syscall access on the server.
- AC:LAttack complexity, low
- A crafted on-disk LZO segment header with seg_len that passes the cbuf-size check but exceeds remaining compressed_len deterministically drives copy_compressed_segment past the last bio folio; no race, special memory layout, or rare kernel config is required.
- PR:NPrivileges required, none
- Triggering needs only read access to btrfs content on an already-mounted/exported volume (e.g., NFS/ksmbd read); planting malformed LZO segment metadata is done via offline btrfs image crafting and does not require init-namespace root or a local account on the victim.
- UI:NUser interaction, none
- Exploitation is the attacker's own read against a btrfs volume that already contains the crafted LZO-compressed extent (backup restore, shared storage, or export); no separate victim mount, click, or plug-in action is needed beyond that read.
- S:UScope, unchanged
- Impact is a kernel NULL-pointer dereference and oops in the btrfs-endio workqueue on the host parsing attacker-supplied compressed data; this is standard host-kernel failure within one security authority, not VM escape or IOMMU bypass.
- C:NConfidentiality impact, none
- The demonstrated failure is a null-ptr-deref read at address 0 in folio_size(NULL) when walking past the bio; unlike slab OOB reads in related btrfs LZO bugs, no adjacent kernel memory is disclosed before the fault.
- I:NIntegrity impact, none
- The bug faults during folio iteration before completing an out-of-bounds copy or decompression; there is no demonstrated or plausible kernel heap/stack write, control-flow hijack, or other integrity corruption beyond attacker-controlled on-disk bytes already in the bio.
- A:HAvailability impact, high
- The NULL dereference in lzo_decompress_bio runs in btrfs-endio kworker context and produces a KASAN-reported kernel oops/panic; any process read (local or remote via NFS/ksmbd) of the crafted extent can repeatedly crash the host.