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

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.

Published: 2025-01-20 Last update: 2025-11-03 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-21655 is rated Low Risk (20.6/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.02%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-21655

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-02-28 0.05% 0.02% -0.03%
2 2025-11-16 0.05% 0.05% +0.00%
3 2025-10-25 — 0.05% —

Full EPSS history (5 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21655

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
4.7 3.1 MEDIUM
CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:H)
Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.0 3.6 [email protected]

Weakness enumeration for CVE-2025-21655

OS Trackers for CVE-2025-21655

vendor priority summary link
debian unimportant CVE-2025-21655 unimportant priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2025-21655
redhat medium — https://access.redhat.com/security/cve/CVE-2025-21655
suse medium CVE-2025-21655 severity moderate: SUSE including 418 source package names (2.1.3-4.43:kernel-default-base-6.4.0-24.1.21.4, 2.1.3-6.5:kernel-default-6.4.0-25.1, …), 811 product×package rows across 145 product lines (Container suse/sl-micro/6.0/base-os-container, Container suse/sl-micro/6.0/kvm-os-container, … (145 product lines)): Fixed 362, Known Affected 231, Known Not Affected 218. https://www.suse.com/security/cve/CVE-2025-21655/
ubuntu medium CVE-2025-21655 medium priority: Ubuntu including 150 source packages (linux, linux-allwinner-5.19, …), 1487 status rows across 10 suites (bionic, focal, jammy, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 1097, ignored 147, released 128, not-affected 115. https://ubuntu.com/security/CVE-2025-21655

Affected software / configurations for CVE-2025-21655

Vendor Product Version Raw CPE
linux linux_kernel >= 6.1, < 6.1.125 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.72 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.10 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc1:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc2:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc3:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc4:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc5:*:*:*:*:*:*
linux linux_kernel 6.13 cpe:2.3:o:linux:linux_kernel:6.13:rc6:*:*:*:*:*:*

References for CVE-2025-21655

cvelogic Threat Intelligence