VulnerabilityPublished 22 Aug 2026Updated 9 Oct 2026

CVE-2026-74657: Linux kernel · ipv4: Fix fib_nlmsg_size() for RTA_VIA nexthops

Affects Linux kernelSource GCVE Database

Not known to be exploited · fixed in 5.15.0-1117.124~20.04.1 : update Linux kernel when convenient.

Data as of 26 Oct 2026, 13:47 UTC

Severity

Medium

Rated by Threat Radar · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 5.15.0-1117.124~20.04.1, 5.15.0-1123.132~20.04.1, 5.15.0-1122.131~20.04.1 +26

Exploitation evidence

Disclosed: evidence found.
CVE published 22 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

ghsa-9gv9-cg8w-rc25

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
Ubuntu 26.04 LTSlinux`pkg:deb/ubuntu/linux?arch=source&distro=resolute`Other threats	Affected 6.17.0-5.5 – 7.0.0-38.38 23 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-aws`pkg:deb/ubuntu/linux-aws?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure`pkg:deb/ubuntu/linux-azure?arch=source&distro=resolute`Other threats	Affected 6.17.0-1003.3 – 7.0.0-1017.17 15 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-azure-fde`pkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resolute`Other threats	Affected 7.0.0-1003.3 – 7.0.0-1016.16 9 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gcp`pkg:deb/ubuntu/linux-gcp?arch=source&distro=resolute`Other threats	Affected 6.17.0-1002.2 – 7.0.0-1014.14 13 affected builds	Fixed in–
Ubuntu 26.04 LTSlinux-gke`pkg:deb/ubuntu/linux-gke?arch=source&distro=resolute`Other threats	Affected 7.0.0-1002.3 – 7.0.0-1008.9 6 affected builds	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

An official fix is available and should be applied. Users should update to patched Linux kernel versions that include the fix for CVE-2026-74657. No additional mitigation steps are required beyond applying the update.

Description

A vulnerability in the Linux kernel's IPv4 routing message size calculation was fixed. The function fib_nlmsg_size() incorrectly estimated the size needed for route notifications when IPv4 routes carried IPv6 gateways, causing allocation of buffers that were too small. This could lead to failures in route notification processing and kernel warnings, which with certain kernel settings could cause a kernel panic. The issue was addressed by adjusting fib_nlmsg_size() to correctly account for IPv6 nexthop gateways and related routing attributes.

Impact

The vulnerability could cause route notification failures and kernel warnings, which under certain kernel configurations (panic_on_warn enabled) could lead to a kernel panic, resulting in a denial of service. There is no indication of privilege escalation or remote code execution. No known exploits in the wild have been reported.

Summary

The Linux kernel vulnerability CVE-2026-74657 involved the fib_nlmsg_size() function miscalculating the size of netlink messages for IPv4 routes that include IPv6 gateways encoded as RTA_VIA attributes. This miscalculation caused route notifications to allocate insufficient buffer space, leading to fib_dump_info() failures with -EMSGSIZE and triggering WARN_ON() conditions in rtmsg_fib(). When the kernel is configured with panic_on_warn, this results in a kernel panic. The fix involved updating fib_nlmsg_size() to mirror the actual nexthop dump layout, properly accounting for IPv6 gateways, no-header rtnexthop layouts, and conditional RTA_FLOW attributes.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 25 Oct 2026, 05:36 UTC

Technical details

References

Community reviews

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