VulnerabilityPublished 25 Apr 2026Updated 6 Nov 2026

CVE-2026-31684: Linux kernel · net: sched: act_csum: validate nested VLAN headers

Affects Linux kernelSource CVE Database V5

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Not known to be exploited · fixed in ec4930979b3f7bbeb7af5744599fc6603a4dba62 : update Linux kernel when convenient.

Data as of 6 Nov 2026, 15:49 UTC

Severity

Unrated

Rated by Threat Radar · No CVSS score from NVD or the CNA

Thin evidence

One scorer or none

Exploitation: No evidence of active exploitation and no public proof of concept
Automatable: Attackers cannot reliably automate steps 1–4 of the kill chain
Technical impact: Limited control over the software or limited information exposure

CISA SSVC assessment, 2026-11-06.

Patch

Available – fixed in ec4930979b3f7bbeb7af5744599fc6603a4dba62, eb3765b90eb8f2a3d6310a80c14a9e57ec4267a2, c842743d073bdd683606cb414eb0ca84465dd834 +6

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 6 Nov 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected >=4.19.99 <4.20	Fixed in ec4930979b3f7bbeb7af5744599fc6603a4dba62 eb3765b90eb8f2a3d6310a80c14a9e57ec4267a2 c842743d073bdd683606cb414eb0ca84465dd834 a69738efea0996d05a3c7d2178551b891744df1b 886469b6455611a511aa6013e957e15e50577513 0410c619e86551677fb79887a38eccad3f5a0725 46c07ad50fa2f4ba7663ee1b72b75ad7ad45cf09 4.20 3d165d975305cf76ff0b10a3c798fb31e5f5f9a5
LinuxLinux	Affected =5.1	Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: net: sched: act_csum: validate nested VLAN headers tcf_csum_act() walks nested VLAN headers directly from skb->data when an skb still carries in-payload VLAN tags. The current code reads vlan->h_vlan_encapsulated_proto and then pulls VLAN_HLEN bytes without first ensuring that the full VLAN header is present in the linear area. If only part of an inner VLAN header is linearized, accessing h_vlan_encapsulated_proto reads past the linear area, and the following skb_pull(VLAN_HLEN) may violate skb invariants. Fix this by requiring pskb_may_pull(skb, VLAN_HLEN) before accessing and pulling each nested VLAN header. If the header still is not fully available, drop the packet through the existing error path.

References

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