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CVE-2026-63955
mm/vmalloc: do not trigger BUG() on BH disabled context
Published 2026-07-19 (3 months ago) by the Linux kernel CNA. Subsystem mm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-63955 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 | not affected | 6.1.190-1 | Nothing to do. bookworm never shipped the vulnerable code. |
| Debian 13trixie | not affected | 6.12.113-1 | Nothing to do. trixie never shipped the vulnerable code. |
| 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
__get_vm_area_node() currently triggers a BUG() if in_interrupt() returns true. However, in_interrupt() also reports true when BH are disabled. The bridge code can call rhashtable_lookup_insert_fast() with bottom halves disabled: __vlan_add() -> br_fdb_add_local() spin_lock_bh(&br->hash_lock); <-- Disable BH -> fdb_add_local() -> fdb_create() -> rhashtable_lookup_insert_fast() -> kvmalloc() -> vmalloc() -> __get_vm_area_node() -> BUG_ON(in_interrupt()) spin_unlock_bh(&br->hash_lock) this triggers the BUG() despite the caller not being in NMI or hard IRQ context. Replace the in_interrupt() check with in_nmi() || in_hardirq().
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.
mm/vmalloc.c
- What this is
- VMALLOCMAINTAINERS section matched on mm/vmalloc.c · linux-mm@kvack.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
- 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
- 0.49%, higher than 40.6% of all CVEssource
- CISA KEV
- not listedthe KEV catalogue
- Debian urgency
- unimportantsource
- Subsystem
- mm
Upstream fixes
The versions the CNA records as introducing and fixing this, and the commit for each. source
| Introduced | Fixed in | Commit |
|---|---|---|
| 6.19 | 7.0.12 | ad7eff07b625 |
| 6.19 | 7.1 | 04aa71da5f35 |
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
- After kvmalloc gained GFP_ATOMIC vmalloc fallback, reachable rhashtable resize paths run from network packet handling (e.g. bridge FDB learning in RX softirq, VXLAN UDP receive/snoop) and can call __get_vm_area_node() while in_interrupt() is true.
- AC:LAttack complexity, low
- An attacker can reliably trigger the BUG by flooding a reachable bridge/VXLAN interface with many unique source MACs (or equivalent netlink admin operations) to force rhashtable growth and a large GFP_ATOMIC kvmalloc vmalloc fallback.
- PR:NPrivileges required, none
- The highest-impact path needs no kernel privileges: sending crafted L2/overlay packets to a learning bridge or VXLAN endpoint is sufficient; netlink-only paths additionally require CAP_NET_ADMIN but are not the ceiling.
- UI:NUser interaction, none
- Exploitation is fully attacker-driven packet or netlink traffic and does not require any victim user action beyond normal system operation.
- S:UScope, unchanged
- Impact is a host kernel BUG/panic from the mm/vmalloc path; it does not cross a VM, IOMMU, or sandbox security boundary for privilege escalation.
- C:NConfidentiality impact, none
- The failure mode is an intentional BUG_ON() kernel panic with no memory corruption, out-of-bounds access, or information disclosure primitive.
- I:NIntegrity impact, none
- No attacker-controlled memory is modified; the bug only aborts the kernel via BUG() rather than providing a write or code-execution primitive.
- A:HAvailability impact, high
- Hitting BUG_ON(in_interrupt()) in __get_vm_area_node() causes a kernel BUG/oops/panic, producing total loss of system availability.