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CVE-2026-63893
thunderbolt: property: Reject u32 wrap in tb_property_entry_valid()
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem drivers/thunderbolt. Debian urgency: not yet assigned.
What to do, per Debian release
Debian's own status for CVE-2026-63893 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 | 6.1.176-1 | Update the kernel and reboot. Fixed in 6.1.176-1. A running kernel keeps the old code until the machine restarts. |
| Debian 13trixie | fixed | 6.12.94-1 | Update the kernel and reboot. Fixed in 6.12.94-1. A running kernel keeps the old code until the machine restarts. |
| Debian 14forky | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.0.12-1 | Update the kernel and reboot. Fixed in 7.0.12-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
entry->value is u32 and entry->length is u16; the sum is performed in u32 and wraps. A malicious XDomain peer can pick value = 0xffffff00, length = 0x100 so the sum 0x100000000 wraps to 0 and passes the > block_len check. tb_property_parse() then passes entry->value to parse_dwdata() as a dword offset into the property block, reading attacker-directed memory far past the allocation. For TEXT-typed entries with the "deviceid" or "vendorid" keys this lands in xd->device_name / xd->vendor_name and is readable back via the per-XDomain device_name / vendor_name sysfs attributes; the leak is NUL-bounded (kstrdup() stops at the first zero byte) and untargeted (the attacker picks a delta, not an absolute address). DATA-typed entries are parsed into property->value.data but not generically surfaced to userspace. Use check_add_overflow() so a wrapped sum is rejected.
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/thunderbolt/property.c
- What this is
- THUNDERBOLT DRIVERMAINTAINERS section matched on drivers/thunderbolt/ · linux-usb@vger.kernel.org · Maintained
Show whether Debian builds this, per release
Not established. This site could not find the build rule for the affected file in the kernel trees Debian ships, so it has no answer about whether Debian compiles this code. Read that as unknown, never as absent.
- bookworm, trixie, forky, sid?
- ?
- not established - no Makefile entry for the affected file
Where a release above reads "not established", no build rule for the affected file was found in that release's kernel tree. That is a gap in this lookup, not a finding that the code is absent.
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
Signals
- Published
- 2026-07-19 (3 months ago)source
- CVSS
- 8.1 high
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:Hsource recompute it - Attack vector
- adjacent network (AV:A)source
- EPSS
- 0.39%, higher than 31.1% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- not yet assignedsource
- Subsystem
- drivers/thunderbolt
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 4.15 | 5.10.259 | 6a6362362163 |
| 4.15 | 5.15.210 | e8a0b0a93a6e |
| 4.15 | 6.1.176 | 9fee50c4e1e4 |
| 4.15 | 6.6.143 | 8d4a758b407a |
| 4.15 | 6.12.93 | 5c06a3043ad9 |
| 4.15 | 6.18.35 | 31b98e503ecc |
| 4.15 | 7.0.12 | a47784aee77f |
| 4.15 | 7.1 | 01deda015206 |
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
- A malicious Thunderbolt XDomain peer (adjacent host, dock, or in-line device on a direct Thunderbolt/USB4 link) delivers crafted PROPERTIES_RESPONSE data that the victim kernel parses during automatic XDomain discovery.
- AC:LAttack complexity, low
- The peer fully controls property entry value/length fields and can reliably craft the u32 wrap (e.g. value=0xffffff00, length=0x100) without races or special memory layout.
- PR:NPrivileges required, none
- Exploitation requires no privileges on the victim system; the attacker only needs to be the connected XDomain peer responding to the kernel-initiated property exchange, with no authentication on that control-plane path.
- UI:NUser interaction, none
- Once a Thunderbolt XDomain link exists, property fetching and parsing run automatically in the kernel handshake state machine without any additional victim user action at exploitation time.
- S:UScope, unchanged
- Impact is confined to the victim kernel/userspace boundary (kernel heap disclosure to local sysfs and possible kernel crash); it does not cross VM, IOMMU, or sandbox security boundaries.
- C:HConfidentiality impact, high
- Integer-wrap bypass enables an out-of-bounds kernel memory read of up to entry->length dwords, which for deviceid/vendorid TEXT properties is copied into world-readable sysfs attributes, disclosing kernel heap contents.
- I:NIntegrity impact, none
- The bug is an out-of-bounds read via parse_dwdata(); destination buffers are properly sized kcalloc allocations, so there is no out-of-bounds write or integrity modification of victim kernel structures.
- A:HAvailability impact, high
- Reading from block+0xffffff00 dwords (~4 GB past the allocation) will access unmapped kernel addresses, causing a kernel fault/oops/panic in addition to any information disclosure.