CVE-2025-21958 [Medium] | Security Vulnerability in Linux Kernel

In the Linux kernel, the following vulnerability has been resolved: Revert "openvswitch: switch to per-action label counting in conntrack" Currently, ovs_ct_set_labels() is only called for confirmed conntrack entries (ct) within ovs_ct_commit(). However, if the conntrack entry does not have the labels_ext extension, attempting to allocate it in ovs_ct_get_conn_labels() for a confirmed entry triggers a warning in nf_ct_ext_add(): WARN_ON(nf_ct_is_confirmed(ct)); This happens when the conntrack entry is created externally before OVS increments net->ct.labels_used. The issue has become more likely since commit fcb1aa5163b1 ("openvswitch: switch to per-action label counting in conntrack"), which changed to use per-action label counting and increment net->ct.labels_used when a flow with ct action is added. Since there’s no straightforward way to fully resolve this issue at the moment, this reverts the commit to avoid breaking existing use cases.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-10	0.02%	0.07%	+0.05%
2	2025-04-02	—	0.02%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-10

0.02%

0.07%

+0.05%

2025-04-02

—

0.02%

—

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]

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]

OS Trackers for CVE-2025-21958

vendor	priority	summary	link
`debian`	unimportant	CVE-2025-21958 unimportant priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2025-21958
`redhat`	low	—	https://access.redhat.com/security/cve/CVE-2025-21958
`suse`	medium	CVE-2025-21958 severity moderate: SUSE including 52 source package names (cluster-md-kmp-default, dlm-kmp-default, …), 267 product×package rows across 45 product lines (SLES-LTSS-TERADATA 15 SP2, SUSE Linux Enterprise High Performance Computing 15 SP3-LTSS, … (45 product lines)): Known Not Affected 241, Fixed 26.	https://www.suse.com/security/cve/CVE-2025-21958/
`ubuntu`	medium	CVE-2025-21958 medium priority: Ubuntu including 130 source packages (linux, linux-allwinner-5.19, …), 1040 status rows across 8 suites (bionic, focal, jammy, noble, oracular, trusty, upstream, xenial): DNE 713, ignored 146, not-affected 117, released 64.	https://ubuntu.com/security/CVE-2025-21958

Affected software / configurations for CVE-2025-21958

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 6.12, < 6.12.20	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.13, < 6.13.8	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc1::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc2::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc3::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc4::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc5::::::
linux	linux_kernel	6.14	cpe:2.3:o:linux:linux_kernel:6.14:rc6::::::

References for CVE-2025-21958

URL	Tags
https://git.kernel.org/stable/c/1063ae07383c0ddc5bcce170260c143825846b03	Patch
https://git.kernel.org/stable/c/9e79fdabd52cfce1a021640a81256878a2c516a2	Patch
https://git.kernel.org/stable/c/d91bfc64a4886102746e74d2c6f3a61e9a77fd7d	Patch

URL

CVE-2025-21958 | Revert "openvswitch: switch to per-action label counting in conntrack"

Exploit prediction scoring system (EPSS) score for CVE-2025-21958

Common vulnerability scoring system (CVSS) metrics for CVE-2025-21958

Weakness enumeration for CVE-2025-21958

OS Trackers for CVE-2025-21958

Affected software / configurations for CVE-2025-21958

References for CVE-2025-21958