Linux Kernel up to 7.1.8 Direct Page Table Reclaim zap_pte_range control flow

Summaryinfo

A vulnerability categorized as very critical has been discovered in Linux Kernel up to 7.1.8. This impacts the function zap_pte_range of the component Direct Page Table Reclaim. The manipulation results in control flow. This vulnerability was named CVE-2026-74674. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in Linux Kernel up to 7.1.8. It has been classified as very critical. Affected is the function zap_pte_range of the component Direct Page Table Reclaim. The manipulation with an unknown input leads to a control flow vulnerability. CWE is classifying the issue as CWE-670. The code contains a control flow path that does not reflect the algorithm that the path is intended to implement, leading to incorrect behavior any time this path is navigated. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

In the Linux kernel, the following vulnerability has been resolved: mm: fix incorrect flush address in direct page table reclaim 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

The advisory is available at git.kernel.org. This vulnerability is traded as CVE-2026-74674 since 08/15/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 08/22/2026).

Upgrading to version 7.1.9 eliminates this vulnerability. Applying the patch 0b8ff21cbda8808c86b18f1b0ca2d0025af9a80a/478a1c3abebfc717db0d1281a9cdd7befafee542 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

Version

• 7.1.0
• 7.1.1
• 7.1.2
• 7.1.3
• 7.1.4
• 7.1.5
• 7.1.6
• 7.1.7
• 7.1.8

License

• open-source

Website

• Vendor: https://www.kernel.org/

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Entryinfo

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