CVE Intelligence
Medium

CVE-2025-21766 — ipv4: use RCU protection in __ip_rt_update_pmtu()

In the Linux kernel, the following vulnerability has been resolved: ipv4: use RCU protection in __ip_rt_update_pmtu() __ip_rt_update_pmtu() must use RCU protection to make sure the net structure it reads does not disappear.

Published Feb 27, 2025 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: Linux

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.5% (30-day exploitation probability)+7
  • Technical severity (medium)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.54%
ahead of 44% of scored CVEs · Oct 14, 2026
Affects
Linux
Linux and 1 more
CVSS base
5.5
Medium · 3 source(s)
Prioritization reference: 8.1 provisional

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)
  • Documented patch — git.kernel.org (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

  1. Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
  2. Apply the fixed version or the patch documented under Remediation.
  3. Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

VendorProductVersionsStatusSource
Linux Linux ≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < ce3c6165fce0f06305c806696882a3ad4b90e33fversion 5.9≥ 5.8.12 and < 5.9≥ 5.4.68 and < 5.5≥ 4.19.148 and < 4.20≥ 4.14.200 and < 4.15version 2b1be6c925cdf4638811765a9160796291494b89version 860e2cc78c697c95bc749abb20047239fa1722ea
and 7 more version 98776a365da509ad923083ae54b38ee521c52742version f415c264176e6095e9dee823e09c5bdd0ee0d337≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < 139512191bd06f1b496117c76372b2ce372c9a41≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < a39f61d212d822b3062d7f70fa0588e50e55664e≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < 4583748b65dee4d61bd50a2214715b4237bc152a≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < 9b1766d1ff5fe496aabe9fc5f4e34e53f35c11c4≥ 2fbc6e89b2f1403189e624cabaf73e189c5e50c6 and < ea07480b23225942208f1b754fea1e7ec486d37e
Vulnerable CVE Program (cve.org) e CISA ADP
Linux Linux Kernel ≥ 4.14.200 and < 4.15version 6.14-rc2version 6.14-rc1version 5.9-rc8version 5.9-rc7version 5.9≥ 6.13 and < 6.13.4≥ 6.7 and < 6.12.16
and 6 more ≥ 6.2 and < 6.6.79≥ 5.16 and < 6.1.129≥ 5.9.1 and < 5.15.179≥ 5.8.12 and < 5.9≥ 5.4.68 and < 5.5≥ 4.19.148 and < 4.20
Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

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

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
8.1 CVSS 3.1 High 2.2 5.9 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
8.1 CVSS 3.1 High — — Linux via CVE Program (cve.org) e CISA ADP
5.5 CVSS 3.1 Medium 1.8 3.6 nvd@nist.gov via NIST National Vulnerability Database
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)
Scoring entities (NIST, CNA, ADP) score independently; each score is shown with its origin. For prioritization we use 8.1 (416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database) as a conservative provisional reference — not a definitive official score.

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
endpoint telemetry (EDR)

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · linux/linux
    Oct 15, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 15, 2026
  • Fix documented
    Oct 15, 2026 · NIST National Vulnerability Database
  • CVSS changed · 5.5
    Oct 15, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 15, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 15, 2026 · NIST National Vulnerability Database
  • 2025
  • CVE published
    Feb 27, 2025 · Linux

Source activity

Repeated readings are counted rather than listed.

  • 1× Official description updated · Oct 15, 2026 – Oct 15, 2026

References

9 on the record

Elsewhere on this site

Linux
every CVE for this vendor

Related CVEs (same products)

  • CVE-2026-99999 ipv4: validate checksum_start before completing checksum 8h
  • CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 8h
  • CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
  • CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
  • CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
  • CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

  • No CISA SSVC assessment.
  • No CWE classification.
  • No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
  • No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
  • No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2025-21766 is "ipv4: use RCU protection in __ip_rt_update_pmtu()", rated Medium. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.54% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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