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CVE-2026-74674
mm: fix incorrect flush address in direct page table reclaim
Published 2026-08-22 (2 months ago) by the Linux kernel CNA. Subsystem mm. Debian urgency: unimportant.
What to do, per Debian release
Debian's own status for CVE-2026-74674 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 | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
| Debian unstablesid | fixed | 7.1.9-1 | Update the kernel and reboot. Fixed in 7.1.9-1. A running kernel keeps the old code until the machine restarts. |
The vulnerability
What the bug is
When zap_pte_range reclaims a page table, it does: pte_free_tlb(tlb, pmd_pgtable(pmdval), addr); and this is unconditionally wrong: if this code executes, addr *always* points one past the end of the range covered by the table. The addr parameter is used to flush the TLB (really the paging-structure-cache) to drop references to the to-be-freed table, and any architecture that cares about the parameter will flush the wrong address. (But they'll still free the correct page). I think it's worth contemplating why the kernel works at all. If we hit the offending line of code, we will first clear the PMD entry (line 1954, zap_empty_pte_table), then we will issue pending flushes if force_flush is set (tlb_flush_mmu_tlbonly(tlb)), then we will skip the retry on line 1979 (phew!), and then we will do the offending pte_free_tlb call. *Or* we will clear the PMD entry immediately before pte_free_tlb (line 1983, zap_pte_table_if_empty). If we have any pending flushes (i.e. we actually zapped any last-level entries) at the time we clear the PMD entry, then the flush really ought to flush all references to the table (Linus certainly seems to think it will on all architectures [0]). The condition under which we have no accumulated flushes at the time of the clear is very complex (the whole zap_pte_range function has absurdly complex control flow). If we do hit the bad case, then we will end up clearing the PMD entry after the last time the range is flushed, and any CPU is free to cache a reference to the (empty) page table. If this happens due to an ordinary read or write, it would segfault, so it would be rare. But the cache could be speculatively filled as well. Then we'll flush the wrong address and then free and possibly reuse the table. On x86, even flushing the wrong address works on non-KPTI Intel systems because INVLPG flushes *all* paging-structure-caches, not just the ones for the target address. But INVPCID does not, and flush_tlb_one_user will use INVPCID if it's available. And then we're toast. AMD systems are more susceptible: we set the EFER.TCE bit, which makes even INVLPG only flush the target address. I think this might fix an issue in ripgrep reported here: https://github.com/BurntSushi/ripgrep/issues/3494 [0] https://lore.kernel.org/all/CA+55aFzBggoXtNXQeng5d_mRoDnaMBE5Y+URs+PHR67nUpMtaw@mail.gmail.com/T/#u
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/memory.c
- What this is
- MEMORY MANAGEMENT - COREMAINTAINERS section matched on mm/memory.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
- 2026-08-22 (2 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
- 0.17%, higher than 5.4% 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 |
|---|---|---|
| 7.0 | 7.1.9 | 0b8ff21cbda8 |
| 7.0 | 7.2 | 478a1c3abebf |
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 bug is only reachable via local memory-management syscalls—primarily madvise(MADV_DONTNEED) on anonymous mappings—that drive zap_pte_range() page-table reclaim; there is no network, adjacent-radio, or physical-device path to this code.
- AC:LAttack complexity, low
- An unprivileged attacker can repeatedly mmap and madvise(DONTNEED) 2MB+ anonymous regions and run concurrent memory pressure (as in the ripgrep repro) to hit the faulty pte_free_tlb() flush; attacker-controlled syscalls and threading make triggering the bad case feasible rather than dependent on uncontrollable system state.
- PR:LPrivileges required, low
- Exploitation requires only a local unprivileged user manipulating their own address space through standard madvise/mmap syscalls; no root, capabilities beyond normal UID, or authentication is needed, and this works within user namespaces on the caller's mm.
- UI:NUser interaction, none
- No victim interaction is required; the attacker directly issues the syscalls and memory-access patterns that cause incorrect paging-structure-cache flushes during PTE page reclaim.
- S:UScope, unchanged
- Impact is stale paging-structure-cache entries and corrupted virtual-to-physical translations within the attacker's process and kernel MM subsystem—standard local memory corruption, not a VM escape, IOMMU bypass, or cross-authority sandbox breakout.
- C:HConfidentiality impact, high
- Flushing the wrong address leaves CPUs with cached references to freed PTE pages; once reused, stale translations can map unrelated physical pages into the attacker's address space, giving arbitrary read primitives and information disclosure consistent with use-after-free severity.
- I:HIntegrity impact, high
- Freed page-table pages can be reallocated while stale paging-structure caches still reference them, enabling wrong virtual-to-physical mappings and demonstrated user-space memory corruption (ripgrep/musl heap corruption), exploitable for arbitrary writes and control-flow hijacking.
- A:HAvailability impact, high
- Stale TLB/paging-structure-cache entries after incorrect flushes cause user-space SIGSEGV (demonstrated in ripgrep on Linux 7.0) and can destabilize or crash affected workloads; memory-corruption class bugs in the MM path carry high availability impact even when not fully weaponized.