CVE-2026-64294: mm: do file ownership checks with the proper mount idmap
Vulnerability summary
CVE-2026-64294 is a medium (CVSS 5.5) vulnerability in linux. EPSS estimates a 0.16% chance of exploitation in the next 30 days, higher than 5.1% of scored vulnerabilities.
Not severe (CVSS 5.5, local access); no exploitation reported by the 5 checked sources
Source freshness unavailable
How is this decided?Advisory lineage
Upstream 0 · Downstream 25 · Related 26Timeline
- 25-07-2026PublishedVulnerability first disclosed.
- 23-08-2026Last modifiedVulnerability information updated.
Description
In the Linux kernel, the following vulnerability has been resolved: mm: do file ownership checks with the proper mount idmap Ever since idmapped mounts were introduced, inode ownership checks (for side-channel protection) in mincore() and madvise(MADV_PAGEOUT) were done against the nop_mnt_idmap, which completely ignores the file's mount's idmap. This results in odd edgecases like: 1) mount/bind-mount with an idmap userA:userB:1 2) userB runs an owner_or_capable() check on file that is owned by userA on-disk/in-memory, but owned by userB after idmap translation 3) owner_or_capable() mysteriously fails as the correct idmap wasn't supplied In the case of mincore/madvise MADV_PAGEOUT, this is usually benign, because file_permission(file, MAY_WRITE) will probably succeed, as it uses the proper idmap internally, but it does not need to be the case on e.g a 0444 file where even the owner itself doesn't have permissions to write to it. Since this is clearly not trivial to get right, introduce a file_owner_or_capable() that can carry the correct semantics, and switch the various users in mm to it. The issue was found by manual code inspection & an off-list discussion with Jan Kara.
CVSS metrics
3 scores · 3 sources · 1 version- OSV · UbuntuEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- OSV · DebianEcosystem advisory · calculated5.5MediumCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
EPSS trend
Probability
0.16%
Chance of exploitation in the next 30 days
Percentile
5%
Versus all other CVEs
30-day change
No change 0.00 pp
From 0.16% on 04-10-2026
Known exploited
Compare KEV catalogs
CISA KEVNot in the CISA KEV catalog.
ENISA CNWNot in the ENISA CNW catalog.
CIRCLNot in the CIRCL catalog.
Public exploits
0 foundNo public exploits indexed.
Weaknesses
CWE · root causeNo weakness data has been published for this record.
Affected systems
Known conditions: local access, low-privilege account, no user interaction (CVSS vector). Other conditions: not stated in public data.
Ubuntu157 products
- linuxAll versions (No fix recorded) | < 6.8.0-147.147 | < 7.0.0-31.31
- linux-allwinner-5.19All versions (No fix recorded)
- linux-awsAll versions (No fix recorded) | < 6.8.0-1067.70 | < 7.0.0-1012.12
- linux-aws-5.0All versions (No fix recorded)
- linux-aws-5.11All versions (No fix recorded)
Chainguard2 products
- linux-gcp-6.18< 6.18.44-r0
- linux-gcp-6.18-bootc< 6.18.44-r0
Debian2 products
- linux< 6.1.187-1 | < 6.12.96-1 | < 7.1.4-1
- linux-6.12< 6.12.100-1~deb12u1
Linux2 products
- linux≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < 7368bec565bac3e536cd43579dbde1e715e6ba61 | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < b2f3d94ea310bea9d36d53e9d9b3f45e86c1d893 | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < 744b23aa430d52f5c8e4dbff7d71496d6643bed2 | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < 8344bdf0629457e532797b42d9d2bbf2a2900bbf | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < 5c942ad7df75925ee166e7f0fb36892d8dde376b | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < 04ba248d02d9eaa3d9077b00a6134caa75fa3e90 | ≥ 9caccd41541a6f7d6279928d9f971f6642c361af, < e187bc02f8fa4226d62814592cf064ee4557c470 | 5.12
- linux_kernel≥ 5.12, < 6.6.145 | ≥ 6.7, < 6.12.96 | ≥ 6.13, < 6.18.39 | ≥ 6.19, < 7.1.4 | 7.2:rc1 | 7.2:rc2
4 vendors · 163 products
