Description
In the Linux kernel, the following vulnerability has been resolved:

binfmt_misc: set have_execfd only once the interpreter is opened

load_misc_binary() raises bprm->have_execfd as soon as it sees the 'O'
(or 'C') flag. This happens well before it opens the interpreter. If
that open fails the flag stays set on the bprm. binfmt_misc is at the
head of the format list so an interpreter open failure that returns
-ENOEXEC lets the search fall through to a later format. This means it
runs the matched binary directly having never staged an interpreter. So
bprm->executable is NULL while have_execfd falsely claims a descriptor
is present.

Consequently, begin_new_exec() dereferences the missing executable:

would_dump(bprm, bprm->executable);

and NULL derefs. Had it not, the hand-off later in the same function
would have failed anyway. FD_ADD(0, bprm->executable) rejects a NULL
file with -ENOMEM. Both sites are past the point of no return so the
exec cannot be unwound either way.

This can be reached by unprivileged users as binfmt_misc can be mounted
in user namespaces. So a user can register an 'O' entry whose
interpreter lives on a FUSE mount, have the FUSE server fail the open
with -ENOEXEC and execute a native ELF file that matches the entry.

have_execfd only means anything alongside the executable it describes
which is not set until the interpreter has been opened and staged.
So lets raise it there, next to execfd_creds, which is already set at
that point. An open failure now leaves it clear, so the fallback format
derives credentials from the binary and emits no AT_EXECFD, as it would
for any native exec. The argv rewrite load_misc_binary() performs before
the open is still not undone. This means the binary sees the interpreter
path in argv[0] and its own path in argv[1] but that predates this
change and only became observable once the exec stopped faulting.
Published: 2026-08-10
Score: 5.5 Medium
EPSS: < 1% Very Low
KEV: No
Impact: n/a
Action: n/a
AI Analysis

Impact

The Linux kernel contains a flaw in the binfmt_misc handling of executable files. A helper flag is set too early during the execution of a binary that is matched against a binfmt_misc entry. If the interpreter specified in the entry fails to open, the flag incorrectly remains set while the real executable pointer is still NULL. Subsequent kernel code improperly dereferences this NULL pointer, causing a kernel crash. The flaw manifests as a null pointer dereference and results in a denial of service for the affected system. The weakness is a classic instance of missing validation before use, matching CWE‑476.

Affected Systems

All Linux kernel installations that allow binfmt_misc to be mounted in user namespaces are impacted. The bug is present in any kernel version that includes the current binfmt_misc implementation and has not applied the fix referenced in the provided commit ranges. Users who rely on this kernel to run user‑defined interpreter formats are at risk.

Risk and Exploitability

Unprivileged local users can mount binfmt_misc anonymously within a user namespace, register an executable type that points to an interpreter on, for example, a FUSE mount, and force the interpreter open to fail with -ENOEXEC. This failure leaves the kernel in an inconsistent state where a NULL executable pointer is used. Because the vulnerability is triggered by a normal execution path and does not require elevated privileges, the attack vector is local, unprivileged. The vulnerability is not listed in the CISA KEV catalog and the EPSS score is < 1%, indicating a low probability of exploitation. However, given the local nature of the attack and the kernel crash outcome, the risk to affected systems remains high, though the CVSS score of 5.5 denotes moderate severity.

Generated by OpenCVE AI on August 13, 2026 at 07:00 UTC.

Remediation

No vendor fix or workaround currently provided.

OpenCVE Recommended Actions

  • Upgrade the kernel to a release that includes the binfmt_misc patch
  • If upgrading is not immediately feasible, disable binfmt_misc mounting in user namespaces or restrict access to the /dev/binfmt_misc interface
  • Configure the system to restrict binfmt_misc mounts to privileged users only and apply appropriate SELinux / AppArmor profiles to prevent unprivileged mounts

Generated by OpenCVE AI on August 13, 2026 at 07:00 UTC.

Tracking

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Advisories
Source ID Title
Debian DLA Debian DLA DLA-4745-1 linux-6.12 security update
History

Wed, 19 Aug 2026 16:45:00 +0000

Type Values Removed Values Added
References

Wed, 12 Aug 2026 00:15:00 +0000

Type Values Removed Values Added
References
Metrics threat_severity

None

 cvssV3_1

{'score': 5.5, 'vector': 'CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H'}

threat_severity

Moderate

Mon, 10 Aug 2026 18:45:00 +0000

Type Values Removed Values Added
Weaknesses CWE-476

Mon, 10 Aug 2026 12:30:00 +0000

Type Values Removed Values Added
Description In the Linux kernel, the following vulnerability has been resolved: binfmt_misc: set have_execfd only once the interpreter is opened load_misc_binary() raises bprm->have_execfd as soon as it sees the 'O' (or 'C') flag. This happens well before it opens the interpreter. If that open fails the flag stays set on the bprm. binfmt_misc is at the head of the format list so an interpreter open failure that returns -ENOEXEC lets the search fall through to a later format. This means it runs the matched binary directly having never staged an interpreter. So bprm->executable is NULL while have_execfd falsely claims a descriptor is present. Consequently, begin_new_exec() dereferences the missing executable: would_dump(bprm, bprm->executable); and NULL derefs. Had it not, the hand-off later in the same function would have failed anyway. FD_ADD(0, bprm->executable) rejects a NULL file with -ENOMEM. Both sites are past the point of no return so the exec cannot be unwound either way. This can be reached by unprivileged users as binfmt_misc can be mounted in user namespaces. So a user can register an 'O' entry whose interpreter lives on a FUSE mount, have the FUSE server fail the open with -ENOEXEC and execute a native ELF file that matches the entry. have_execfd only means anything alongside the executable it describes which is not set until the interpreter has been opened and staged. So lets raise it there, next to execfd_creds, which is already set at that point. An open failure now leaves it clear, so the fallback format derives credentials from the binary and emits no AT_EXECFD, as it would for any native exec. The argv rewrite load_misc_binary() performs before the open is still not undone. This means the binary sees the interpreter path in argv[0] and its own path in argv[1] but that predates this change and only became observable once the exec stopped faulting.
Title binfmt_misc: set have_execfd only once the interpreter is opened
First Time appeared Linux
Linux linux Kernel
CPEs cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Vendors & Products Linux
Linux linux Kernel
References

Subscriptions

Linux Linux Kernel
cve-icon MITRE

Status: PUBLISHED

Assigner: Linux

Published:

Updated: 2026-08-19T16:30:54.269Z

Reserved: 2026-07-30T09:28:09.373Z

Link: CVE-2026-68186

cve-icon Vulnrichment

No data.

cve-icon NVD

Status : Received

Published: 2026-08-10T13:20:05.740

Modified: 2026-08-19T17:20:34.727

Link: CVE-2026-68186

cve-icon Redhat

Severity : Moderate

Publid Date: 2026-08-10T00:00:00Z

Links: CVE-2026-68186 - Bugzilla

cve-icon OpenCVE Enrichment

Updated: 2026-08-13T07:15:12Z

Weaknesses