VulnerabilityPublished 25 Sep 2026Updated 19 Oct 2026

CVE-2026-98104: Linux kernel · net/sched: cls_u32: fix duplicate handle when node ID pool is exhausted

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in feab9261b537df4ebb8350e4779bc185373059fd : update Linux kernel when convenient.

Data as of 26 Oct 2026, 12:55 UTC

Severity

Medium

Rated Medium by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.2% chance of exploitation in 30 days – higher than 10% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in feab9261b537df4ebb8350e4779bc185373059fd, f594f04268d01c5fdc975f3f51fc219ea2159ac6, f4ee13ed7f7b22dcd8287fcf477ae37bd84567da +3

Exploitation evidence

Disclosed: evidence found.
CVE published 25 Sep 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.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < feab9261b537df4ebb8350e4779bc185373059fd	Fixed in feab9261b537df4ebb8350e4779bc185373059fd
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < f594f04268d01c5fdc975f3f51fc219ea2159ac6	Fixed in f594f04268d01c5fdc975f3f51fc219ea2159ac6
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < f4ee13ed7f7b22dcd8287fcf477ae37bd84567da	Fixed in f4ee13ed7f7b22dcd8287fcf477ae37bd84567da
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f	Fixed in d7e7e98d23f42a92d9ab7e36302bd96bd9b33b5f
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < 84223baf21bc9b008444ae9bc38d5fb91fe00b9d	Fixed in 84223baf21bc9b008444ae9bc38d5fb91fe00b9d
LinuxLinux	Affected ≥ 7801db8aec957fa6610efe0ee26a6c8bc0f1d73b, < 6890e28840bae4f6805e8de981c4ec8e12a4e064	Fixed in 6890e28840bae4f6805e8de981c4ec8e12a4e064

AI-suggested

A fix is available in the Linux kernel commits identified by the fixedVersions hashes. Users should update to a kernel version including these fixes to prevent duplicate handle creation when node ID pools are exhausted. No additional mitigation is required beyond applying the official patch.

Description

CVE-2026-98104 is a vulnerability in the Linux kernel's net/sched cls_u32 module where duplicate handles can be created when the node ID pool is exhausted. This occurs because the function gen_new_kid() returns a fallback handle value instead of reporting an error when ID ranges are full, causing handle uniqueness to break. Similarly, gen_new_htid() can return 0 when the handle pool is full, leading to aliasing of root tables. This flaw can be triggered by adding a large number of u32 filters or proto entries, causing collisions and potential cross-protocol node manipulation.

Impact

The impact is a violation of handle uniqueness within the cls_u32 hash table, which can lead to corruption of the scheduling filter state. This may allow manipulation or interference between different filter nodes, potentially affecting network traffic classification and filtering behavior. The vulnerability requires specific conditions to trigger (filling node ID pools), and is reachable with namespace-local CAP_NET_ADMIN privileges. No public exploits or in-the-wild exploitation are known.

Summary

The vulnerability in the Linux kernel's net/sched cls_u32 subsystem arises from improper handling of node ID pool exhaustion. The function gen_new_kid() silently returns a fallback handle value (max (htid | 0xFFF)) when ID allocation fails, leading to insertion of duplicate handles in the hash table. This breaks the uniqueness invariant and causes erroneous removal of live nodes, compounding duplicates. Similarly, gen_new_htid() returns 0 when the handle pool is full, causing root tables to alias and enabling cross-tcf_proto knode operations. The fix involves returning explicit errors (ENOSPC or -ENOMEM) when the node ID or handle pools are exhausted, preventing duplicate handle insertion and aliasing.

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 12:42 UTC

Technical details

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