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CVE-2026-74656· NVD / CVE Program· CNA Linux

ipv4: fix use-after-free in fib_nhc_update_mtu()

Noroxi assessment

Priority: Monitor (action score 31/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.12% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 3.17, 4.10, 4.15; azl3 kernel 6.6.150.1-1 on Azure Linux 3.0 6.6.152.1-1.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 3.17, 4.10, 4.15; azl3 kernel 6.6.150.1-1 on Azure Linux 3.0 6.6.152.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: ipv4: fix use-after-free in fib_nhc_update_mtu() fib_nhc_update_mtu() walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. The walk uses rcu_dereference_protected() with a constant true condition without holding fnhe_lock. The following interleaving can therefore occur: CPU 0 CPU 1 fib_nhc_update_mtu() update_or_create_fnhe() load fnhe spin_lock_bh(&fnhe_lock) fnhe_remove_oldest() unlink fnhe kfree_rcu(fnhe, rcu) <quiescent state> access fnhe after grace period KASAN reported: BUG: KASAN: slab-use-after-free in fib_nhc_update_mtu+0x3df/0x410 Read of size 8 at addr ffff888107d49000 by task poc/90 Call Trace: fib_nhc_update_mtu+0x3df/0x410 fib_sync_mtu+0x7a/0xd0 fib_netdev_event+0x229/0x3f0 netif_set_mtu_ext+0x33a/0x570 dev_set_mtu+0x88/0x120 The same walk updates fnhe_pmtu and fnhe_mtu_locked. These fields form a pair and other writers serialize them with fnhe_lock. RCU alone prevents reclamation, but would still allow concurrent writers to leave a mixed pair. Walk the table under RCU and acquire fnhe_lock only while updating each exception. RCU keeps the current entry alive while the short critical section serializes its paired PMTU fields. This avoids holding the global lock while scanning all 2048 buckets for every nexthop.

HighCVSS 7.8 · v3.1—No exploit Fix available
Published
Aug 22, 2026
Updated
Oct 14, 2026
EPSS
0.1% · 2th percentile
CWE
—

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.1%

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • No public exploit code on record
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

—

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • b427832009b97a3ee412ef643a80b15372a7754d, 2b7e4c735933be79882aba2bed9afa789e03c62f, 8d59c3a6376bbc6dd3f7303968a719ffba75a4f1, 9b4869cf385aa16f89c0f019eed4ec4e36aa441c, ff34695ced21e2dfa04d0fa1c5f6c35011fa8117, 4.19affected
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before fd39e711866498ae94fcf9acf6f422a4f045b681affected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before e1e602d6b22d5cb1641c4459c487eb18bf569e0aaffected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before e00f7d2b5f2540a3415a229c982af7a25ff6362eaffected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before dfe388da13aa784851e5ebbea90afbb099075761affected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before 5a28a4b22dde92f9d293b94236314b8d6181dc4aaffected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before 63996ffc594d128ccec8fc0983f91effd2d3adc4affected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before ed503eaad62f20cdd5122d7c3078a648a99c8f16affected · git
    • af7d6cce53694a88d6a1bb60c9a239a6a5144459 and later · before bc5bde9ce3cc36502839dfe98e068f7303a50982affected · git
    • 3.16.62 and later · before 3.17affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 6.1.187-16.1.187-1
Debian:12linux-6.12before 6.12.107-1~deb12u16.12.107-1~deb12u1
Debian:13linuxbefore 6.12.105-16.12.105-1
Debian:14linuxbefore 7.1.9-17.1.9-1

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-74705udp: fix potential use-after-free in tunnel segmentation
    40Plan
  • CVE-2026-74612veth: fix skb length accounting after XDP frag adjustment
    40Plan
  • CVE-2026-74475vxlan: use neigh_ha_snapshot() in route_shortcircuit()
    40Plan
  • CVE-2026-74309vdpa/octeon_ep: fix IRQ-to-ring mapping in interrupt handler
    40Plan
  • CVE-2026-74280crypto: marvell/octeontx - fix DMA cleanup using wrong loop index
    40Plan
  • CVE-2026-74279crypto: cavium/cpt - fix DMA cleanup using wrong loop index
    40Plan

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux3.17Vendor (CNA)
Linux Linux4.10Vendor (CNA)
Linux Linux4.15Vendor (CNA)
Linux Linux4.19Vendor (CNA)
Linux Linux4.5Vendor (CNA)
Linux Linux5a28a4b22dde92f9d293b94236314b8d6181dc4aVendor (CNA)
Linux Linux63996ffc594d128ccec8fc0983f91effd2d3adc4Vendor (CNA)
Linux Linuxbc5bde9ce3cc36502839dfe98e068f7303a50982Vendor (CNA)
Linux Linuxdfe388da13aa784851e5ebbea90afbb099075761Vendor (CNA)
Linux Linuxe00f7d2b5f2540a3415a229c982af7a25ff6362eVendor (CNA)
Linux Linuxe1e602d6b22d5cb1641c4459c487eb18bf569e0aVendor (CNA)
Linux Linuxed503eaad62f20cdd5122d7c3078a648a99c8f16Vendor (CNA)
Linux Linuxfd39e711866498ae94fcf9acf6f422a4f045b681Vendor (CNA)
azl3 kernel 6.6.150.1-1 on Azure Linux 3.06.6.152.1-1 · Release NotesMicrosoft (MSRC)
debian:linux6.1.187-1 · Debian:12Package registry (OSV)
debian:linux-6.126.12.107-1~deb12u1 · Debian:12Package registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

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Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

—

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (7 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records