high 7.8

CVE-2025-21655 json

io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

published 2025-01-20 21 mo ago modified 2026-10-15 25 d ago also EUVD-2025-2604

cvss: 7.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 16%
public exploits: 0; none known

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

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.

Patch / fix

fixed in 1 distros 6 links 4

Linux Linux 6.1.125, 6.6.72, 6.12.10, 6.13

debian ubuntu red hat suse almalinux rocky linux

linux Debian 12 6.1.128-1
linux Debian 14, Debian 13 6.12.10-1

debian advisories DEBIAN-CVE-2025-21655

linux Ubuntu 24.04 LTS 6.8.0-60.63
linux-aws Ubuntu 24.04 LTS 6.8.0-1029.31
linux-gcp Ubuntu 24.04 LTS 6.8.0-1030.32
linux-gke Ubuntu 24.04 LTS 6.8.0-1025.29
linux-ibm Ubuntu 24.04 LTS 6.8.0-1026.26
linux-azure Ubuntu 24.04 LTS 6.8.0-1029.34
linux-gkeop Ubuntu 24.04 LTS 6.8.0-1012.14
linux-raspi Ubuntu 24.04 LTS 6.8.0-1028.32

ubuntu advisories UBUNTU-CVE-2025-21655

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

kernel RHEL 10.1 6.12.0-124.8.1.el10_1
rv RHEL 10.1 6.12.0-124.8.1.el10_1
perf RHEL 10.1 6.12.0-124.8.1.el10_1
rtla RHEL 10.1 6.12.0-124.8.1.el10_1
libperf RHEL 10.1 6.12.0-124.8.1.el10_1
kernel-rt RHEL 10.1 6.12.0-124.8.1.el10_1
kernel-64k RHEL 10.1 6.12.0-124.8.1.el10_1
kernel-core RHEL 10.1 6.12.0-124.8.1.el10_1

red hat advisories RHSA-2025:20095

kernel-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-source-rt Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-livepatch-MICRO-6-0-RT_Update_5 Linux Micro 6.1, Linux Micro 6.0 1-1.1
kernel-source Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-default Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-kvmsmall Linux Micro 6.1, Linux Micro 6.0 6.4.0-25.1
kernel-default-base Linux Micro 6.1, Linux Micro 6.0 6.4.0-24.1.21.4
kernel-livepatch-MICRO-6-0_Update_5 Linux Micro 6.1, Linux Micro 6.0 1-1.2

suse advisories SUSE-SU-2025:20166-1 SUSE-SU-2025:20249-1 SUSE-SU-2025:20165-1 SUSE-SU-2025:20248-1 SUSE-SU-2025:0564-1 SUSE-SU-2025:0557-1

kernel AlmaLinux 10 6.12.0-124.8.1.el10_1
rv AlmaLinux 10 6.12.0-124.8.1.el10_1
perf AlmaLinux 10 6.12.0-124.8.1.el10_1
rtla AlmaLinux 10 6.12.0-124.8.1.el10_1
libperf AlmaLinux 10 6.12.0-124.8.1.el10_1
kernel-rt AlmaLinux 10 6.12.0-124.8.1.el10_1
kernel-64k AlmaLinux 10 6.12.0-124.8.1.el10_1
kernel-core AlmaLinux 10 6.12.0-124.8.1.el10_1

almalinux advisories ALSA-2025:20095

kernel Rocky Linux 10 6.12.0-124.8.1.el10_1

rocky linux advisories RLSA-2025:20095

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-21655 updated 2026-11-07

kernel: io_uring/eventfd: ensure io_eventfd_signal() defers another RCU period

Red Hat Enterprise Linux AppStream (v. 10) rv 6.12.0-124.8.1.el10_1, perf 6.12.0-124.8.1.el10_1, rtla 6.12.0-124.8.1.el10_1, python3-perf 6.12.0-124.8.1.el10_1, kernel-devel-matched 6.12.0-124.8.1.el10_1, kernel-64k-devel-matched 6.12.0-124.8.1.el10_1, +7 more Red Hat Enterprise Linux BaseOS (v. 10) kernel 6.12.0-124.8.1.el10_1, kernel-64k 6.12.0-124.8.1.el10_1, kernel-core 6.12.0-124.8.1.el10_1, kernel-tools 6.12.0-124.8.1.el10_1, kernel-modules 6.12.0-124.8.1.el10_1, kernel-64k-core 6.12.0-124.8.1.el10_1, +28 more Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) libperf 6.12.0-124.8.1.el10_1, kernel-debuginfo-common-s390x 6.12.0-124.8.1.el10_1, kernel-debuginfo-common-x86_64 6.12.0-124.8.1.el10_1, kernel-debuginfo-common-aarch64 6.12.0-124.8.1.el10_1, kernel-debuginfo-common-ppc64le 6.12.0-124.8.1.el10_1 Red Hat Enterprise Linux Real Time (v. 10) kernel-rt 6.12.0-124.8.1.el10_1, kernel-rt-64k 6.12.0-124.8.1.el10_1, kernel-rt-core 6.12.0-124.8.1.el10_1, kernel-rt-modules 6.12.0-124.8.1.el10_1, kernel-rt-64k-core 6.12.0-124.8.1.el10_1, kernel-rt-debug-core 6.12.0-124.8.1.el10_1, +14 more Red Hat Enterprise Linux Real Time for NFV (v. 10) kernel-rt 6.12.0-124.8.1.el10_1, kernel-rt-core 6.12.0-124.8.1.el10_1, kernel-rt-modules 6.12.0-124.8.1.el10_1, kernel-rt-debug-core 6.12.0-124.8.1.el10_1, kernel-rt-modules-core 6.12.0-124.8.1.el10_1, kernel-rt-debug-modules 6.12.0-124.8.1.el10_1, +4 more
fixed: vendor fix RHSA-2025:20095
Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-295-11 updated 2026-10-22 cvss 7.8

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.7 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.7
affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-26-209-04 updated 2026-07-28 cvss 4.7

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.6 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.6
affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.25% chance of exploitation in the next 30 days, higher than 16% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	7.8	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
NVD	3.1	4.7	CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

Linux Linux
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness

CWE-416 Use After Free

Technology feeds

Linux kernel rss critical rss

References

Sources

CVE List CVE-2025-21655
NVD CVE-2025-21655

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary