CVE-2026-89493
In the Linux kernel, the following vulnerability has been resolved:
ocfs2: validate rl_used against rl_count in refcount block validator
ocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array with:
rl_recs[] lives in a single metadata block (4096 bytes on the common configuration), so its real capacity is fixed by ocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the 16-byte ocfs2_refcount_rec). rl_used and rl_count are both read directly off disk by ocfs2_validate_refcount_block() and are never checked against that capacity, nor against each other, before any refcount/reflink/CoW operation walks the array.
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A crafted (or corrupted) refcount block with rl_used == 0xffff makes the loop above walk far past the end of the block, dereferencing rl_recs[i] for i up to 65534. The resulting index is then handed to the sibling ocfs2_insert_refcount_rec(), whose insert-shift does:
if (index < le16_to_cpu(rf_list->rl_used)) memmove(&rf_list->rl_recs[index + 1], &rf_list->rl_recs[index], (le16_to_cpu(rf_list->rl_used) - index) * sizeof(struct ocfs2_refcount_rec));
i.e. a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an offset already past the block. This is reachable from an ordinary reflink (FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent whose cpos sorts past every real record in the leaf forces the lookup to run off the end instead of returning early on a match. The attacker model is local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a raw write to the block device backing an already-mounted ocfs2 filesystem.
ocfs2_validate_refcount_block() already validates the block's ECC, signature, rf_blkno and rf_fs_generation, but never rl_count/rl_used against the block's actual on-disk capacity. This is the same class of gap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes for the sibling extent-list header, which checks both the record capacity and the "used" bound before any code walks h_list.l_recs[]:
Add the equivalent pair of checks to ocfs2_validate_refcount_block(): reject a refcount block whose rl_count does not match the fixed per-block capacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used > rl_count. Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set, because in that case the same union bytes hold an ocfs2_extent_list (rf_list), not the refcount record list (rf_records) -- that layout is already validated separately by ocfs2_validate_extent_block() when the referenced extent block is read. This mirrors the existing "!(rb->rf_flags & OCFS2_REFCOUNT_TREE_FL)" guard used elsewhere in this file (e.g. ocfs2_get_refcount_rec()) to decide whether rf_records or rf_list is the live member of the union.
With this in place, a forged rl_used/rl_count is caught at block validation time (ocfs2_error()), consistent with every other corruption check in this function, instead of driving an out-of-bounds read in ocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove() in ocfs2_insert_refcount_rec().
Verified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build: replaying the same reflink (FICLONE) reliably hit a KASAN report in __ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch, and triggers no report once ocfs2_validate_refcount_block() rejects the forged rl_used/rl_count.
Detalles técnicos trazas, registros y código del informe original
for (; i < le16_to_cpu(rb->rf_records.rl_used); i++) {
rec = &rb->rf_records.rl_recs[i];
...
if (le16_to_cpu(eb->h_list.l_count) != ocfs2_extent_recs_per_eb(sb)) {
rc = ocfs2_error(...);
goto bail;
}
if (le16_to_cpu(eb->h_list.l_next_free_rec) >
le16_to_cpu(eb->h_list.l_count)) {
rc = ocfs2_error(...);
goto bail;
}CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 8.8
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.65%
- Percentil entre todas las CVEs puntuadas: 49
- Fecha de la puntuación: 6/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1210Exploitation of Remote Serviceslateral movement60 %
Inferido por reglas deterministas a partir del vector CVSS y la CWE. Solo orientativo.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.
Referencias
- https://git.kernel.org/stable/c/04ead708e13ddcb9c39319cbe02a18cef99cb823
- https://git.kernel.org/stable/c/0761d2c9494424469a0d30a9da3496ca010b0b2d
- https://git.kernel.org/stable/c/4ca62df6bc0708947b48da3f6a712ecb8e73929c
- https://git.kernel.org/stable/c/5593b63028cb43a6cda75a65ce1db95f00ea6857
- https://git.kernel.org/stable/c/97584e93fc49a2d59252ac60467e9279f11b1b5b
- https://git.kernel.org/stable/c/af56e90cb546cb0c47bef059335365283f61d6a4
- https://git.kernel.org/stable/c/c8b02f4ee91e757b3fff556c7168b24b7ae55132
- https://git.kernel.org/stable/c/f882e9e32d017a6569b2996c63ba3864717788e6
JSON original (NVD)
Mostrar
{
"id": "CVE-2026-89493",
"cveTags": [],
"metrics": {
"cvssMetricV31": [
{
"type": "Secondary",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"cvssData": {
"scope": "UNCHANGED",
"version": "3.1",
"baseScore": 8.8,
"attackVector": "NETWORK",
"baseSeverity": "HIGH",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
"integrityImpact": "HIGH",
"userInteraction": "NONE",
"attackComplexity": "LOW",
"availabilityImpact": "HIGH",
"privilegesRequired": "LOW",
"confidentialityImpact": "HIGH"
},
"impactScore": 5.9,
"exploitabilityScore": 2.8
}
]
},
"affected": [
{
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"affectedData": [
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "f882e9e32d017a6569b2996c63ba3864717788e6",
"versionType": "git"
},
{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "5593b63028cb43a6cda75a65ce1db95f00ea6857",
"versionType": "git"
},
{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "c8b02f4ee91e757b3fff556c7168b24b7ae55132",
"versionType": "git"
},
{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "97584e93fc49a2d59252ac60467e9279f11b1b5b",
"versionType": "git"
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{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
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{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "0761d2c9494424469a0d30a9da3496ca010b0b2d",
"versionType": "git"
},
{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "04ead708e13ddcb9c39319cbe02a18cef99cb823",
"versionType": "git"
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{
"status": "affected",
"version": "f2c870e3b12e38da6d9b5b17c4c8ae56a0ed68e4",
"lessThan": "4ca62df6bc0708947b48da3f6a712ecb8e73929c",
"versionType": "git"
}
],
"programFiles": [
"fs/ocfs2/refcounttree.c"
],
"defaultStatus": "unaffected"
},
{
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"product": "Linux",
"versions": [
{
"status": "affected",
"version": "2.6.32"
},
{
"status": "unaffected",
"version": "0",
"lessThan": "2.6.32",
"versionType": "semver"
},
{
"status": "unaffected",
"version": "5.10.270",
"versionType": "semver",
"lessThanOrEqual": "5.10.*"
},
{
"status": "unaffected",
"version": "5.15.221",
"versionType": "semver",
"lessThanOrEqual": "5.15.*"
},
{
"status": "unaffected",
"version": "6.1.188",
"versionType": "semver",
"lessThanOrEqual": "6.1.*"
},
{
"status": "unaffected",
"version": "6.6.157",
"versionType": "semver",
"lessThanOrEqual": "6.6.*"
},
{
"status": "unaffected",
"version": "6.12.109",
"versionType": "semver",
"lessThanOrEqual": "6.12.*"
},
{
"status": "unaffected",
"version": "6.18.50",
"versionType": "semver",
"lessThanOrEqual": "6.18.*"
},
{
"status": "unaffected",
"version": "7.2.4",
"versionType": "semver",
"lessThanOrEqual": "7.2.*"
},
{
"status": "unaffected",
"version": "7.3-rc1",
"versionType": "original_commit_for_fix",
"lessThanOrEqual": "*"
}
],
"programFiles": [
"fs/ocfs2/refcounttree.c"
],
"defaultStatus": "affected"
}
]
}
],
"published": "2026-09-11T20:19:31.220",
"references": [
{
"url": "https://git.kernel.org/stable/c/04ead708e13ddcb9c39319cbe02a18cef99cb823",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/0761d2c9494424469a0d30a9da3496ca010b0b2d",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/4ca62df6bc0708947b48da3f6a712ecb8e73929c",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/5593b63028cb43a6cda75a65ce1db95f00ea6857",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/97584e93fc49a2d59252ac60467e9279f11b1b5b",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/af56e90cb546cb0c47bef059335365283f61d6a4",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/c8b02f4ee91e757b3fff556c7168b24b7ae55132",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
},
{
"url": "https://git.kernel.org/stable/c/f882e9e32d017a6569b2996c63ba3864717788e6",
"source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}
],
"vulnStatus": "Received",
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nocfs2: validate rl_used against rl_count in refcount block validator\n\nocfs2_find_refcount_rec_in_rl() walks the on-disk refcount record array\nwith:\n\n\tfor (; i < le16_to_cpu(rb->rf_records.rl_used); i++) {\n\t\trec = &rb->rf_records.rl_recs[i];\n\t\t...\n\nrl_recs[] lives in a single metadata block (4096 bytes on the common\nconfiguration), so its real capacity is fixed by\nocfs2_refcount_recs_per_rb(sb) (247 records for a 4K block with the\n16-byte ocfs2_refcount_rec). rl_used and rl_count are both read directly\noff disk by ocfs2_validate_refcount_block() and are never checked against\nthat capacity, nor against each other, before any refcount/reflink/CoW\noperation walks the array.\n\nA crafted (or corrupted) refcount block with rl_used == 0xffff makes the\nloop above walk far past the end of the block, dereferencing rl_recs[i]\nfor i up to 65534. The resulting index is then handed to the sibling\nocfs2_insert_refcount_rec(), whose insert-shift does:\n\n\tif (index < le16_to_cpu(rf_list->rl_used))\n\t\tmemmove(&rf_list->rl_recs[index + 1],\n\t\t\t&rf_list->rl_recs[index],\n\t\t\t(le16_to_cpu(rf_list->rl_used) - index) *\n\t\t\t sizeof(struct ocfs2_refcount_rec));\n\ni.e. a memmove() of up to (0xffff - index) * 16 bytes (~1 MiB) from an\noffset already past the block. This is reachable from an ordinary reflink\n(FICLONE) against a crafted/corrupted ocfs2 image: attaching an extent\nwhose cpos sorts past every real record in the leaf forces the lookup to\nrun off the end instead of returning early on a match. The attacker model\nis local: CAP_SYS_ADMIN mounting a crafted or corrupted ocfs2 image, or a\nraw write to the block device backing an already-mounted ocfs2 filesystem.\n\nocfs2_validate_refcount_block() already validates the block's ECC,\nsignature, rf_blkno and rf_fs_generation, but never rl_count/rl_used\nagainst the block's actual on-disk capacity. This is the same class of\ngap that ocfs2_validate_extent_block() (fs/ocfs2/alloc.c) already closes\nfor the sibling extent-list header, which checks both the record capacity\nand the \"used\" bound before any code walks h_list.l_recs[]:\n\n\tif (le16_to_cpu(eb->h_list.l_count) != ocfs2_extent_recs_per_eb(sb)) {\n\t\trc = ocfs2_error(...);\n\t\tgoto bail;\n\t}\n\n\tif (le16_to_cpu(eb->h_list.l_next_free_rec) >\n\t le16_to_cpu(eb->h_list.l_count)) {\n\t\trc = ocfs2_error(...);\n\t\tgoto bail;\n\t}\n\nAdd the equivalent pair of checks to ocfs2_validate_refcount_block():\nreject a refcount block whose rl_count does not match the fixed per-block\ncapacity returned by ocfs2_refcount_recs_per_rb(), and reject rl_used >\nrl_count. Both checks are skipped when OCFS2_REFCOUNT_TREE_FL is set,\nbecause in that case the same union bytes hold an ocfs2_extent_list\n(rf_list), not the refcount record list (rf_records) -- that layout is\nalready validated separately by ocfs2_validate_extent_block() when the\nreferenced extent block is read. This mirrors the existing\n\"!(rb->rf_flags & OCFS2_REFCOUNT_TREE_FL)\" guard used elsewhere in this\nfile (e.g. ocfs2_get_refcount_rec()) to decide whether rf_records or\nrf_list is the live member of the union.\n\nWith this in place, a forged rl_used/rl_count is caught at block\nvalidation time (ocfs2_error()), consistent with every other corruption\ncheck in this function, instead of driving an out-of-bounds read in\nocfs2_find_refcount_rec_in_rl() and a subsequent out-of-bounds memmove()\nin ocfs2_insert_refcount_rec().\n\nVerified against a crafted image on a v6.19 KASAN (KASAN_GENERIC) build:\nreplaying the same reflink (FICLONE) reliably hit a KASAN report in\n__ocfs2_increase_refcount()/ocfs2_insert_refcount_rec() before this patch,\nand triggers no report once ocfs2_validate_refcount_block() rejects the\nforged rl_used/rl_count."
}
],
"lastModified": "2026-09-14T13:19:06.250",
"sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}