CVE-2026-90203 (GCVE-0-2026-90203)
Vulnerability from cvelistv5 – Published: 2026-09-17 16:07 – Updated: 2026-10-19 08:59
VLAI
EPSS
VEX
Title
Squashfs: check block offset is not negative
Summary
In the Linux kernel, the following vulnerability has been resolved:
Squashfs: check block offset is not negative
If a negative offset is read off disk (for example the offset into the
decompressed fragment block), this will cause squashfs_copy_data() to
perform an out of bounds access.
Fix by checking if offset is negative, and returning 0. This matches
existing behaviour where an offset beyond the block returns 0 bytes
copied.
To trigger this out of bounds access requires a crafted Squashfs
filesystem and CAP_SYS_ADMIN to mount it. Unprivileged users will not be
able to mount such a filesystem, but once mounted, an unprivileged user
can trigger the out of bounds access by reading the crafted file with the
negative offset.
Severity
7.1 (High)
Assigner
References
8 references
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
f400e12656ab518be107febfe2315fb1eab5a342 , < b169185d5c672b989985c6c2e38cafab2548ba88
(git)
Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < c2a126fca820ae74872da28de68dc74d4595dc4b (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < 95dadf366c117dcdca78a570e6832071deab1ecd (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < 3d2f0cb66c909ea2312cdef465165bb9a3ba2d84 (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < bbb2218eb072b0a15dc063929200183bd23c2344 (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < d0a3729d464fcf516416a41cf304c0c92126ee03 (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < e4afd90bc7bf3dd477970c6c42bdd29ad3fda7fe (git) Affected: f400e12656ab518be107febfe2315fb1eab5a342 , < e300eb5002925b29be803d2661af07266cfa267e (git) |
guessed | |
| Linux | Linux |
Affected:
2.6.29
Unaffected: 0 , < 2.6.29 (semver) Unaffected: 5.10.270 , ≤ 5.10.* (semver) Unaffected: 5.15.221 , ≤ 5.15.* (semver) Unaffected: 6.1.188 , ≤ 6.1.* (semver) Unaffected: 6.6.157 , ≤ 6.6.* (semver) Unaffected: 6.12.110 , ≤ 6.12.* (semver) Unaffected: 6.18.52 , ≤ 6.18.* (semver) Unaffected: 7.2.6 , ≤ 7.2.* (semver) Unaffected: 7.3 , ≤ * (original_commit_for_fix) |
guessed |
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{
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"version": "5.15.221",
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{
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{
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"status": "unaffected",
"version": "6.6.157",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.110",
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},
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{
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"version": "7.2.6",
"versionType": "semver"
},
{
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"status": "unaffected",
"version": "7.3",
"versionType": "original_commit_for_fix"
}
]
}
],
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"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSquashfs: check block offset is not negative\n\nIf a negative offset is read off disk (for example the offset into the\ndecompressed fragment block), this will cause squashfs_copy_data() to\nperform an out of bounds access.\n\nFix by checking if offset is negative, and returning 0. This matches\nexisting behaviour where an offset beyond the block returns 0 bytes\ncopied.\n\nTo trigger this out of bounds access requires a crafted Squashfs\nfilesystem and CAP_SYS_ADMIN to mount it. Unprivileged users will not be\nable to mount such a filesystem, but once mounted, an unprivileged user\ncan trigger the out of bounds access by reading the crafted file with the\nnegative offset."
}
],
"metrics": [
{
"cvssV3_1": {
"baseScore": 7.1,
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H",
"version": "3.1"
},
"scenarios": [
{
"lang": "en",
"value": "AV:L - The bad bytes are squashfs_reg_inode.offset/squashfs_lreg_inode.offset, stored by squashfs_read_inode() as fragment_offset and used by squashfs_read_folio()/squashfs_readahead_fragment() \u2192 squashfs_copy_data() on a loop/block-backed image. That field is on-disk fragment metadata, not a network protocol message; squashfs_fs_type is FS_REQUIRES_DEV.\nAC:L - squashfs_read_inode() assigns le32_to_cpu(sqsh_ino-\u003eoffset) to signed int fragment_offset with no range check, so a high-bit-set on-disk value is negative. read() of that file\u0027s tail (generic_file_read_iter \u2192 squashfs_read_folio) then calls squashfs_copy_data() with that offset; there is no race.\nPR:N - squashfs_fs_type has no FS_USERNS_MOUNT, so mount_capable() needs init-namespace CAP_SYS_ADMIN, but the attacker who crafts the image needs no account. After that privileged mount, an unprivileged read of the crafted file is enough; the mount is scored as User Interaction, not Privileges Required.\nUI:R - The negative fragment_offset exists only in an attacker-supplied Squashfs image, and squashfs_copy_data() runs only after that image is mounted and the crafted file is read. The mount is the required victim action; a standing snapd or live-image setup does not remove it.\nS:U - squashfs_copy_data() indexes the fragment cache\u0027s kmalloc\u0027d data[] array and memcpy\u0027s into the file\u0027s own page-cache folio in the same kernel. This is not a KVM/Xen guest-to-host escape or an IOMMU/DMA bypass.\nC:H - A negative offset makes squashfs_copy_data() evaluate entry-\u003edata[offset/PAGE_SIZE] before the kcalloc\u0027d pointer array, then memcpy up to PAGE_SIZE bytes from that address into the folio returned by read(). That is an unbounded OOB kernel read into userspace, not a few-byte leak.\nI:N - The memcpy destination is the kmap of the crafted file\u0027s own folio in squashfs_fill_page()/squashfs_readahead_fragment(); the source is the OOB pointer. Length is capped by avail (\u2264PAGE_SIZE), so this path does not write kernel objects out of bounds.\nA:H - Indexing entry-\u003edata[] with a negative offset/PAGE_SIZE and memcpy from the resulting pointer is the same squashfs_copy_data() out-of-bounds access that produced a general protection fault in CVE-2026-23388; an unmapped address oopses the kernel."
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-10-19T08:59:39.333Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
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"references": [
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"url": "https://git.kernel.org/stable/c/b169185d5c672b989985c6c2e38cafab2548ba88"
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"url": "https://git.kernel.org/stable/c/c2a126fca820ae74872da28de68dc74d4595dc4b"
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"url": "https://git.kernel.org/stable/c/95dadf366c117dcdca78a570e6832071deab1ecd"
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{
"url": "https://git.kernel.org/stable/c/3d2f0cb66c909ea2312cdef465165bb9a3ba2d84"
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"url": "https://git.kernel.org/stable/c/bbb2218eb072b0a15dc063929200183bd23c2344"
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{
"url": "https://git.kernel.org/stable/c/e4afd90bc7bf3dd477970c6c42bdd29ad3fda7fe"
},
{
"url": "https://git.kernel.org/stable/c/e300eb5002925b29be803d2661af07266cfa267e"
}
],
"title": "Squashfs: check block offset is not negative",
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"cveId": "CVE-2026-90203",
"datePublished": "2026-09-17T16:07:20.180Z",
"dateReserved": "2026-09-11T19:38:34.792Z",
"dateUpdated": "2026-10-19T08:59:39.333Z",
"state": "PUBLISHED"
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"date": "2026-11-01",
"epss": "0.00171",
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"versions": [
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"version": "2.6.29"
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"status": "unaffected",
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"version": "7.2.6",
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"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSquashfs: check block offset is not negative\n\nIf a negative offset is read off disk (for example the offset into the\ndecompressed fragment block), this will cause squashfs_copy_data() to\nperform an out of bounds access.\n\nFix by checking if offset is negative, and returning 0. This matches\nexisting behaviour where an offset beyond the block returns 0 bytes\ncopied.\n\nTo trigger this out of bounds access requires a crafted Squashfs\nfilesystem and CAP_SYS_ADMIN to mount it. Unprivileged users will not be\nable to mount such a filesystem, but once mounted, an unprivileged user\ncan trigger the out of bounds access by reading the crafted file with the\nnegative offset."
}
],
"id": "CVE-2026-90203",
"lastModified": "2026-10-19T09:19:10.377",
"metrics": {
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{
"cvssData": {
"attackComplexity": "LOW",
"attackVector": "LOCAL",
"availabilityImpact": "HIGH",
"baseScore": 7.1,
"baseSeverity": "HIGH",
"confidentialityImpact": "HIGH",
"integrityImpact": "NONE",
"privilegesRequired": "NONE",
"scope": "UNCHANGED",
"userInteraction": "REQUIRED",
"vectorString": "CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:H",
"version": "3.1"
},
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"impactScore": 5.2,
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"type": "Secondary"
}
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},
"published": "2026-09-17T17:17:15.320",
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{
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{
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{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"url": "https://git.kernel.org/stable/c/e4afd90bc7bf3dd477970c6c42bdd29ad3fda7fe"
}
],
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"vulnStatus": "Received"
}
},
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-10-23T03:39:44+00:00",
"cve": "CVE-2026-90203",
"id": "CVE-2026-90203",
"initial_release_date": "2026-09-17T00:00:00+00:00",
"product_status:known_affected": "278",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: Squashfs: check block offset is not negative",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-90203.json",
"version": "3"
}
}
}
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Related by attack behaviour
Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.