CVE-2026-74618 (GCVE-0-2026-74618)
Vulnerability from cvelistv5 – Published: 2026-08-22 15:32 – Updated: 2026-08-22 15:32
VLAI
EPSS
VEX
Title
binfmt_misc: don't warn when the mount is completed from another user namespace
Summary
In the Linux kernel, the following vulnerability has been resolved:
binfmt_misc: don't warn when the mount is completed from another user namespace
fsopen() records the caller's user namespace in fc->user_ns and hands
back an ordinary file descriptor. Nothing ties the task that calls
fsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The
fd is inherited across fork() and exec() and it can be passed over a
unix socket.
Completing a context from another user namespace is allowed on purpose.
vfs_cmd_create() authorizes the create with mount_capable(), which for
FS_USERNS_MOUNT checks ns_capable(fc->user_ns, CAP_SYS_ADMIN), and that
succeeds for a task holding CAP_SYS_ADMIN in an ancestor of fc->user_ns.
So an unprivileged task can reach the WARN_ON() in bm_fill_super():
create a user and a mount namespace in a child, call
fsopen("binfmt_misc") there, send the fscontext fd to the parent and let
the parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain
unshare(1) and no capability is needed anywhere:
WARNING: fs/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc]
CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn
Call Trace:
get_tree_keyed+0x7d/0xb0
bm_get_tree+0x34/0x90 [binfmt_misc]
vfs_get_tree+0x2a/0x100
vfs_cmd_create+0x60/0xf0
__do_sys_fsconfig+0x4b2/0x500
The child needs the mount namespace because fsopen() itself gates on
may_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning
the caller's mount namespace. fsconfig() doesn't repeat that check.
It is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be
raised in a loop to taint the kernel and flood the log, and it panics a
kernel booted with panic_on_warn.
Keep refusing the mount and stop warning about it. Nothing in
bm_fill_super() depends on the two namespaces matching, it derives
everything from sb->s_user_ns.
Severity
No CVSS data available.
Assigner
References
Impacted products
2 products
| Vendor | Product | Version | CPE status | |
|---|---|---|---|---|
| Linux | Linux |
Affected:
21ca59b365c091d583f36ac753eaa8baf947be6f , < 37cf5cf1320a84a17225a1690547b8a0812ca94e
(git)
Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < 24e95a24f151ce40d5fc1b3a6cefbcda8ded736c (git) Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < 047f927f54c6c17593e93aafe82dcb7acdda2a71 (git) Affected: 21ca59b365c091d583f36ac753eaa8baf947be6f , < 79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6 (git) |
guessed | |
| Linux | Linux |
Affected:
6.7
Unaffected: 0 , < 6.7 (semver) Unaffected: 6.12.104 , ≤ 6.12.* (semver) Unaffected: 6.18.45 , ≤ 6.18.* (semver) Unaffected: 7.1.9 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix) |
guessed |
{
"containers": {
"cna": {
"affected": [
{
"defaultStatus": "unaffected",
"product": "Linux",
"programFiles": [
"fs/binfmt_misc.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"lessThan": "37cf5cf1320a84a17225a1690547b8a0812ca94e",
"status": "affected",
"version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
"versionType": "git"
},
{
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"status": "affected",
"version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
"versionType": "git"
},
{
"lessThan": "047f927f54c6c17593e93aafe82dcb7acdda2a71",
"status": "affected",
"version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
"versionType": "git"
},
{
"lessThan": "79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6",
"status": "affected",
"version": "21ca59b365c091d583f36ac753eaa8baf947be6f",
"versionType": "git"
}
]
},
{
"defaultStatus": "affected",
"product": "Linux",
"programFiles": [
"fs/binfmt_misc.c"
],
"repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
"vendor": "Linux",
"versions": [
{
"status": "affected",
"version": "6.7"
},
{
"lessThan": "6.7",
"status": "unaffected",
"version": "0",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.12.*",
"status": "unaffected",
"version": "6.12.104",
"versionType": "semver"
},
{
"lessThanOrEqual": "6.18.*",
"status": "unaffected",
"version": "6.18.45",
"versionType": "semver"
},
{
"lessThanOrEqual": "7.1.*",
"status": "unaffected",
"version": "7.1.9",
"versionType": "semver"
},
{
"lessThanOrEqual": "*",
"status": "unaffected",
"version": "7.2",
"versionType": "original_commit_for_fix"
}
]
}
],
"cpeApplicability": [
{
"nodes": [
{
"cpeMatch": [
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.12.104",
"versionStartIncluding": "6.7",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "6.18.45",
"versionStartIncluding": "6.7",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.1.9",
"versionStartIncluding": "6.7",
"vulnerable": true
},
{
"criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
"versionEndExcluding": "7.2",
"versionStartIncluding": "6.7",
"vulnerable": true
}
],
"negate": false,
"operator": "OR"
}
]
}
],
"descriptions": [
{
"lang": "en",
"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbinfmt_misc: don\u0027t warn when the mount is completed from another user namespace\n\nfsopen() records the caller\u0027s user namespace in fc-\u003euser_ns and hands\nback an ordinary file descriptor. Nothing ties the task that calls\nfsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The\nfd is inherited across fork() and exec() and it can be passed over a\nunix socket.\n\nCompleting a context from another user namespace is allowed on purpose.\nvfs_cmd_create() authorizes the create with mount_capable(), which for\nFS_USERNS_MOUNT checks ns_capable(fc-\u003euser_ns, CAP_SYS_ADMIN), and that\nsucceeds for a task holding CAP_SYS_ADMIN in an ancestor of fc-\u003euser_ns.\nSo an unprivileged task can reach the WARN_ON() in bm_fill_super():\ncreate a user and a mount namespace in a child, call\nfsopen(\"binfmt_misc\") there, send the fscontext fd to the parent and let\nthe parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain\nunshare(1) and no capability is needed anywhere:\n\n WARNING: fs/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc]\n CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn\n Call Trace:\n get_tree_keyed+0x7d/0xb0\n bm_get_tree+0x34/0x90 [binfmt_misc]\n vfs_get_tree+0x2a/0x100\n vfs_cmd_create+0x60/0xf0\n __do_sys_fsconfig+0x4b2/0x500\n\nThe child needs the mount namespace because fsopen() itself gates on\nmay_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning\nthe caller\u0027s mount namespace. fsconfig() doesn\u0027t repeat that check.\n\nIt is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be\nraised in a loop to taint the kernel and flood the log, and it panics a\nkernel booted with panic_on_warn.\n\nKeep refusing the mount and stop warning about it. Nothing in\nbm_fill_super() depends on the two namespaces matching, it derives\neverything from sb-\u003es_user_ns."
}
],
"providerMetadata": {
"dateUpdated": "2026-08-22T15:32:02.778Z",
"orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"shortName": "Linux"
},
"references": [
{
"url": "https://git.kernel.org/stable/c/37cf5cf1320a84a17225a1690547b8a0812ca94e"
},
{
"url": "https://git.kernel.org/stable/c/24e95a24f151ce40d5fc1b3a6cefbcda8ded736c"
},
{
"url": "https://git.kernel.org/stable/c/047f927f54c6c17593e93aafe82dcb7acdda2a71"
},
{
"url": "https://git.kernel.org/stable/c/79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6"
}
],
"title": "binfmt_misc: don\u0027t warn when the mount is completed from another user namespace",
"x_generator": {
"engine": "bippy-1.2.0"
}
}
},
"cveMetadata": {
"assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
"assignerShortName": "Linux",
"cveId": "CVE-2026-74618",
"datePublished": "2026-08-22T15:32:02.778Z",
"dateReserved": "2026-08-15T05:44:03.921Z",
"dateUpdated": "2026-08-22T15:32:02.778Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2",
"vulnerability-lookup:meta": {
"epss": {
"cve": "CVE-2026-74618",
"date": "2026-08-29",
"epss": "0.00168",
"percentile": "0.06298"
},
"nvd": "{\"cve\":{\"id\":\"CVE-2026-74618\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-08-22T16:16:34.507\",\"lastModified\":\"2026-08-22T16:16:34.507\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In the Linux kernel, the following vulnerability has been resolved:\\n\\nbinfmt_misc: don\u0027t warn when the mount is completed from another user namespace\\n\\nfsopen() records the caller\u0027s user namespace in fc-\u003euser_ns and hands\\nback an ordinary file descriptor. Nothing ties the task that calls\\nfsconfig(FSCONFIG_CMD_CREATE) to the task that created the context. The\\nfd is inherited across fork() and exec() and it can be passed over a\\nunix socket.\\n\\nCompleting a context from another user namespace is allowed on purpose.\\nvfs_cmd_create() authorizes the create with mount_capable(), which for\\nFS_USERNS_MOUNT checks ns_capable(fc-\u003euser_ns, CAP_SYS_ADMIN), and that\\nsucceeds for a task holding CAP_SYS_ADMIN in an ancestor of fc-\u003euser_ns.\\nSo an unprivileged task can reach the WARN_ON() in bm_fill_super():\\ncreate a user and a mount namespace in a child, call\\nfsopen(\\\"binfmt_misc\\\") there, send the fscontext fd to the parent and let\\nthe parent issue FSCONFIG_CMD_CREATE. Both namespaces come from a plain\\nunshare(1) and no capability is needed anywhere:\\n\\n WARNING: fs/binfmt_misc.c:938 at bm_fill_super+0xa2/0xc0 [binfmt_misc]\\n CPU: 15 UID: 1000 PID: 3243382 Comm: fswarn\\n Call Trace:\\n get_tree_keyed+0x7d/0xb0\\n bm_get_tree+0x34/0x90 [binfmt_misc]\\n vfs_get_tree+0x2a/0x100\\n vfs_cmd_create+0x60/0xf0\\n __do_sys_fsconfig+0x4b2/0x500\\n\\nThe child needs the mount namespace because fsopen() itself gates on\\nmay_mount(), which asks for CAP_SYS_ADMIN in the user namespace owning\\nthe caller\u0027s mount namespace. fsconfig() doesn\u0027t repeat that check.\\n\\nIt is a WARN_ON() and not a WARN_ON_ONCE(), so the condition can be\\nraised in a loop to taint the kernel and flood the log, and it panics a\\nkernel booted with panic_on_warn.\\n\\nKeep refusing the mount and stop warning about it. Nothing in\\nbm_fill_super() depends on the two namespaces matching, it derives\\neverything from sb-\u003es_user_ns.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"fs/binfmt_misc.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"21ca59b365c091d583f36ac753eaa8baf947be6f\",\"lessThan\":\"37cf5cf1320a84a17225a1690547b8a0812ca94e\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"21ca59b365c091d583f36ac753eaa8baf947be6f\",\"lessThan\":\"24e95a24f151ce40d5fc1b3a6cefbcda8ded736c\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"21ca59b365c091d583f36ac753eaa8baf947be6f\",\"lessThan\":\"047f927f54c6c17593e93aafe82dcb7acdda2a71\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"21ca59b365c091d583f36ac753eaa8baf947be6f\",\"lessThan\":\"79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"fs/binfmt_misc.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.7\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.7\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.12.104\",\"lessThanOrEqual\":\"6.12.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"6.18.45\",\"lessThanOrEqual\":\"6.18.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.9\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/047f927f54c6c17593e93aafe82dcb7acdda2a71\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/24e95a24f151ce40d5fc1b3a6cefbcda8ded736c\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/37cf5cf1320a84a17225a1690547b8a0812ca94e\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/79fdf39f1a31f88cb3833b6f8091fbf6acdca2c6\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
"redhat_vex": {
"aggregate_severity": "Moderate",
"current_release_date": "2026-08-24T14:36:05+00:00",
"cve": "CVE-2026-74618",
"id": "CVE-2026-74618",
"initial_release_date": "2026-08-22T00:00:00+00:00",
"product_status:known_affected": "198",
"product_status:known_not_affected": "76",
"source": "Red Hat CSAF VEX",
"status": "final",
"title": "kernel: binfmt_misc: don\u0027t warn when the mount is completed from another user namespace",
"url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-74618.json",
"version": "3"
}
}
}
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Experimental. This forecast is provided for visualization only and may change without notice. Do not use it for operational decisions.
Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.
Sightings
| Author | Source | Type | Date | Other |
|---|
Nomenclature
- Seen: The vulnerability was mentioned, discussed, or observed by the user.
- Confirmed: The vulnerability has been validated from an analyst's perspective.
- Published Proof of Concept: A public proof of concept is available for this vulnerability.
- Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
- Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
- Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
- Not confirmed: The user expressed doubt about the validity of the vulnerability.
- Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.
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The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the
vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base
model, served locally by ML-Gateway.
They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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