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CVE-2026-64323
udf: validate VAT header length against the VAT inode size
Published 2026-07-25 (3 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-2026-64323 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 | fixedDLA-4720-1 · 2026-08-05 · text | 6.1.180-1 | Update the kernel and reboot. DLA-4720-1 shipped the fix on 2026-08-05, in 6.1.180-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.96-1 | Update the kernel and reboot. Fixed in 6.12.96-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.4-1 | Update the kernel and reboot. Fixed in 7.1.4-1. A running kernel keeps the old code until the machine restarts. |
| Debian 12bookworm · linux-6.12 | fixedDLA-4724-1 · 2026-08-07 · text | 6.12.100-1~deb12u1 | Update the kernel and reboot. DLA-4724-1 shipped the fix on 2026-08-07, in 6.12.100-1~deb12u1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
udf_load_vat() takes the virtual partition's start offset straight from the on-disk VAT 2.0 header without checking it against the VAT inode size: map->s_type_specific.s_virtual.s_start_offset = le16_to_cpu(vat20->lengthHeader); map->s_type_specific.s_virtual.s_num_entries = (sbi->s_vat_inode->i_size - map->s_type_specific.s_virtual.s_start_offset) >> 2; lengthHeader is a fully attacker-controlled 16-bit value. If it exceeds the VAT inode size, the s_num_entries subtraction underflows to a huge count, which defeats the "block > s_num_entries" bound in udf_get_pblock_virt15(); and on the ICB-inline path that function reads ((__le32 *)(iinfo->i_data + s_start_offset))[block] so a large s_start_offset indexes past the inode's in-ICB data. Mounting a crafted UDF image with a virtual (VAT) partition then triggers an out-of-bounds read. Reject a VAT whose header length does not leave room for at least one entry within the VAT inode.
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/super.c
- 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, sid, bookworm · linux-6.12m
- 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
- 2026-07-25 (3 months ago)source
- CVSS
- 7.1 high
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- local (AV:L)source
- EPSS
- 0.16%, higher than 5.3% 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 |
|---|---|---|
| 2.6.26 | 5.10.261 | 0ad2d09a8d66 |
| 2.6.26 | 5.15.212 | 883962731420 |
| 2.6.26 | 6.1.178 | 2900e02a0dd4 |
| 2.6.26 | 6.6.145 | bb0d384c1f42 |
| 2.6.26 | 6.12.96 | 55287a3555ff |
| 2.6.26 | 6.18.39 | e610fb113cdf |
| 2.6.26 | 7.1.4 | 74580fdf0229 |
| 2.6.26 | 7.2 | d8202786b3d7 |
Debian advisories
| Advisory | Date | Shipped to | Debian |
|---|---|---|---|
| DLA-4724-1 | 2026-08-07 | bookworm 6.12.100-1~deb12u1 | tracker |
| DLA-4723-1 | 2026-08-07 | bullseye 6.1.180-1~deb11u1 | tracker |
| DLA-4720-1 | 2026-08-05 | bookworm 6.1.180-1 | tracker |
| DLA-4717-1 | 2026-08-05 | bullseye 5.10.262-1 | 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
- The vulnerable parser is reached by mounting a crafted local UDF image or removable volume; no network-facing protocol reaches it.
- AC:LAttack complexity, low
- The VAT type, inline allocation, header length, and virtual block index are attacker-controlled on disk, with no race or uncontrollable condition required.
- PR:LPrivileges required, low
- Although direct mounting requires init-namespace CAP_SYS_ADMIN, common UDisks/polkit deployments let an active unprivileged local user create a loop device and request the mount.
- UI:NUser interaction, none
- In the low-privilege UDisks scenario, the attacker can initiate the mount and trigger VAT resolution without another user's action.
- S:UScope, unchanged
- The vulnerable UDF parser and affected kernel resources remain within the host kernel's security authority.
- C:HConfidentiality impact, high
- The underflow permits repeatable 32-bit reads at attacker-selected offsets potentially many gigabytes beyond the VAT buffer, enabling disclosure of kernel memory.
- I:NIntegrity impact, none
- The primitive only reads a mapping value, and virtual UDF partitions are forcibly read-only; no kernel-memory write primitive results.
- A:HAvailability impact, high
- A sufficiently large attacker-selected index can fault in kernel context and cause an oops or panic, enabling repeatable system-wide denial of service.