CVE-2026-74656

Kernel memory corruption via unlocked PMTU update race

Published Aug 22, 2026 · Updated Aug 25, 2026

Use-after-free in the Linux kernel IPv4 stack allows local users to corrupt kernel memory by racing MTU and PMTU exception updates. fib_nhc_update_mtu() traverses nexthop exceptions without fnhe_lock, allowing update_or_create_fnhe() to unlink and free an entry before the traversal accesses it. Low-privileged local access suffices because a user and network namespace grants CAP_NET_ADMIN; exploitation can disclose or alter kernel memory or crash the host.

CVSS severity7.8
High
EPSS probability0.13%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in the Linux kernel IPv4 stack allows local users to corrupt kernel memory by racing MTU and PMTU exception updates. fib_nhc_update_mtu() traverses nexthop exceptions without fnhe_lock, allowing update_or_create_fnhe() to unlink and free an entry before the traversal accesses it. Low-privileged local access suffices because a user and network namespace grants CAP_NET_ADMIN; exploitation can disclose or alter kernel memory or crash the host.

The record

CVE
CVE-2026-74656
Published
Aug 22, 2026
Updated
Aug 25, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-367, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 22, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2b7e4c735933be79882aba2bed9afa789e03c62f
  2. Affected versionversion=3.16.62 <3.17
  3. Affected versionversion=4.14.77 <4.15
  4. Affected versionversion=4.18.15 <4.19
  5. Affected versionversion=4.19
  6. Affected versionversion=4.4.162 <4.5
  7. Affected versionversion=4.9.134 <4.10
  8. Affected versionversion=8d59c3a6376bbc6dd3f7303968a719ffba75a4f1
  9. Affected versionversion=9b4869cf385aa16f89c0f019eed4ec4e36aa441c
  10. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <5a28a4b22dde92f9d293b94236314b8d6181dc4a
  11. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <63996ffc594d128ccec8fc0983f91effd2d3adc4
  12. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <bc5bde9ce3cc36502839dfe98e068f7303a50982
  13. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <dfe388da13aa784851e5ebbea90afbb099075761
  14. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e00f7d2b5f2540a3415a229c982af7a25ff6362e
  15. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e1e602d6b22d5cb1641c4459c487eb18bf569e0a
  16. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <ed503eaad62f20cdd5122d7c3078a648a99c8f16
  17. Affected versionversion=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <fd39e711866498ae94fcf9acf6f422a4f045b681
  18. Affected versionversion=b427832009b97a3ee412ef643a80b15372a7754d
  19. Affected versionversion=ff34695ced21e2dfa04d0fa1c5f6c35011fa8117

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=2b7e4c735933be79882aba2bed9afa789e03c62f; version=3.16.62 <3.17; version=4.14.77 <4.15; version=4.18.15 <4.19; version=4.19; version=4.4.162 <4.5; version=4.9.134 <4.10; version=8d59c3a6376bbc6dd3f7303968a719ffba75a4f1; version=9b4869cf385aa16f89c0f019eed4ec4e36aa441c; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <5a28a4b22dde92f9d293b94236314b8d6181dc4a; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <63996ffc594d128ccec8fc0983f91effd2d3adc4; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <bc5bde9ce3cc36502839dfe98e068f7303a50982; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <dfe388da13aa784851e5ebbea90afbb099075761; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e00f7d2b5f2540a3415a229c982af7a25ff6362e; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <e1e602d6b22d5cb1641c4459c487eb18bf569e0a; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <ed503eaad62f20cdd5122d7c3078a648a99c8f16; version=af7d6cce53694a88d6a1bb60c9a239a6a5144459 <fd39e711866498ae94fcf9acf6f422a4f045b681; version=b427832009b97a3ee412ef643a80b15372a7754d; version=ff34695ced21e2dfa04d0fa1c5f6c35011fa8117

Published CVSS scores

7.8Linux CNACVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-367Time-of-check Time-of-use (TOCTOU) Race Condition
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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