NVD / CVE Program· CNA Linux

CVE-2025-21655: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

Noroxi assessment

Priority: Monitor (action score 18/100)

The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
Probability of exploitation in the next 30 days: 0.25% (FIRST EPSS).
Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. Special conditions such as timing or configuration are required.
Fixed version: Linux Linux 6b63308c28987c6010b1180c72a6db4df6c68033, 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10, a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7.
Severity is disputed: the assigning authority (CNA) scores it 7.8, NVD 4.7.

Low priority for now. Upgrade to Linux Linux 6b63308c28987c6010b1180c72a6db4df6c68033, 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10, a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period io_eventfd_do_signal() is invoked from an RCU callback, but when dropping the reference to the io_ev_fd, it calls io_eventfd_free() directly if the refcount drops to zero. This isn't correct, as any potential freeing of the io_ev_fd should be deferred another RCU grace period. Just call io_eventfd_put() rather than open-code the dec-and-test and free, which will correctly defer it another RCU grace period.

MediumCVSS 4.7 · v3.1—No exploit Fix available

BDU:2025-06557

Published: Jan 20, 2025
Updated: Oct 15, 2026
EPSS: 0.2% · 16th percentile
CWE: CWE-416

Report tools

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Action score

Monitor

Low priority for now.

CVSS: 18 / 40 · 4.7 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 0 / 30 · 0.2%

CNA vs NVD score

NVD: 4.7
CNA · Linux: 7.8; 3.1 point gap

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
No public exploit code on record
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
linux	linux kernel	cpe:2.3:o:linux:linux_kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

linux linux kernel6.1 and later · before 6.1.125
linux linux kernel6.2 and later · before 6.6.72
linux linux kernel6.7 and later · before 6.12.10
linux linux kernel6.13

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

Linux Linux
- 6.1affected
- 21a091b970cdbcf3e8ff829234b51be6f9192766 and later · before 6b63308c28987c6010b1180c72a6db4df6c68033affected · git
- 21a091b970cdbcf3e8ff829234b51be6f9192766 and later · before 8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10affected · git
- 21a091b970cdbcf3e8ff829234b51be6f9192766 and later · before a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7affected · git
- 21a091b970cdbcf3e8ff829234b51be6f9192766 and later · before c9a40292a44e78f71258b8522655bffaf5753bdbaffected · git
- before 6.1not affected · semver
- 6.1.125 and later · up to and including 6.1.*not affected · semver
- 6.6.72 and later · up to and including 6.6.*not affected · semver
- 6.12.10 and later · up to and including 6.12.*not affected · semver
- 6.13 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
Debian:12	linux	before 6.1.128-1	6.1.128-1
Debian:13	linux	before 6.12.10-1	6.12.10-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
90Now
CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
89Now
CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
85Now

Published before and after this one in the same product

← EarlierCVE-2024-57929Jan 19, 2025 · dm array: fix releasing a faulty array block twice in dm_array_cursor_end
28Monitor
← EarlierCVE-2023-52923Jan 20, 2025 · netfilter: nf_tables: adapt set backend to use GC transaction API
22Monitor
Later →CVE-2024-57930Jan 21, 2025 · tracing: Have process_string() also allow arrays
22Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Linux Linux	6b63308c28987c6010b1180c72a6db4df6c68033	Vendor (CNA)
Linux Linux	8efff2aa2d95dc437ab67c5b4a9f1d3f367baa10	Vendor (CNA)
Linux Linux	a7085c3ae43b86d4b3d1b8275e6a67f14257e3b7	Vendor (CNA)
Linux Linux	c9a40292a44e78f71258b8522655bffaf5753bdb	Vendor (CNA)
debian:linux	6.1.128-1 · Debian:12	Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

Someone with local access to the system can trigger it.
A low-privileged account is enough.
No user action is required.
Special conditions such as timing or configuration are required.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Local
Attack complexity: High
Privileges required: Low
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1free(dev->buf);
2/* ... another thread is still running ... */
3process(dev->buf);

Fixed

1lock(&dev->lock);
2free(dev->buf);
3dev->buf = NULL;
4unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

Fix✗ → ✓Sep 28, 2026, 10:11 PM UTC

For records you follow, these changes also arrive as notifications. →

References

git.kernel.org/stable/c/6b63308c28987c6010b1180c72a6db4df6c68033

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records