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CVE-2024-50211
udf: refactor inode_bmap() to handle error
Published 2024-11-08 (23 months ago) by the Linux kernel CNA. Subsystem fs/udf. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2024-50211 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 | fixed | 6.11.6-1 | Update the kernel and reboot. Fixed in 6.11.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 6.11.6-1 | Update the kernel and reboot. Fixed in 6.11.6-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 6.11.6-1 | Update the kernel and reboot. Fixed in 6.11.6-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
Refactor inode_bmap() to handle error since udf_next_aext() can return error now. On situations like ftruncate, udf_extend_file() can now detect errors and bail out early without resorting to checking for particular offsets and assuming internal behavior of these functions.
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/udf/directory.c
fs/udf/inode.c
fs/udf/partition.c
fs/udf/truncate.c
fs/udf/udfdecl.h
- What this is
- UDF FILESYSTEMMAINTAINERS section matched on fs/udf/ · Maintained
- Kernel module
- udf
Check it on the machine
grep -w CONFIG_UDF_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 udfPrints 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_UDF_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
- 2024-11-08 (23 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
- 0.21%, higher than 11.0% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- fs/udf
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 2.6.12 | 6.6.59 | 493447dd8336 |
| 2.6.12 | 6.11.6 | b22d9a5698ab |
| 2.6.12 | 6.12 | c226964ec786 |
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
- Exploitation requires local access to mount a crafted UDF filesystem image (loop device, USB stick, or optical disc) and then issue an ftruncate()/truncate() syscall against a file on it. There is no remote or network-facing path into fs/udf.
- AC:LAttack complexity, low
- The attacker fully controls the on-disk UDF metadata (indirect extent chains, lengthAllocDescs, extent locations pointing past device capacity) that forces udf_next_aext() into its error paths, and syzbot produced a deterministic C reproducer; no race and no uncontrollable memory-layout precondition is involved.
- PR:LPrivileges required, low
- On mainstream Linux desktops an active unprivileged user can loop-setup and mount a crafted UDF image via udisks2/polkit (allow_active by default) or have removable UDF media automounted, and only ordinary write access to a file is needed to call ftruncate(); no real root in the initial namespace is required in that deployment.
- UI:NUser interaction, none
- The attacker performs both steps — supplying/mounting the image and issuing the ftruncate() — with no action by any other user in the unprivileged-loop-mount scenario.
- S:UScope, unchanged
- The out-of-bounds read and write occur in kernel slab memory within the same security authority; no VM, IOMMU, or sandbox boundary is crossed.
- C:HConfidentiality impact, high
- The confirmed KASAN slab-out-of-bounds read pulls adjacent kernel heap contents into extent.extLength/extLocation, which are then written into the file's allocation descriptors on the attacker-readable image and used as block addresses, disclosing kernel memory and arbitrary device blocks.
- I:HIntegrity impact, high
- The same corrupted extent_position flows into udf_write_aext()/__udf_add_aext(), which write an 8–16 byte allocation descriptor through an unchecked ptr = i_data + epos->offset - alloc_offset + lenEAttr, giving an out-of-bounds slab write with attacker-influenced offset and data — a heap corruption primitive suitable for control-flow hijacking.
- A:HAvailability impact, high
- The out-of-bounds access reliably produces a KASAN/oops kernel crash, and the corrupted i_lenExtents plus huge computed new_elen drive udf_do_extend_file() into unbounded extent creation, so an unprivileged local user can panic or hang the system.