VulnerabilityPublished 17 Sep 2026Updated 30 Oct 2026

CVE-2026-90076: Linux kernel · net/sched: fq: add overflow bounds to quantum and initial quantum

Source GCVE Database

Compare

Authoritative record:CVE-2026-90076· High

Not known to be exploited · fixed in fd63409b669f9951f1cc6b02486a5254103800d1 : patch Linux kernel soon.

Data as of 30 Oct 2026, 19:20 UTC

Severity

High

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

Thin evidence

One scorer or none

Patch: Available – fixed in fd63409b669f9951f1cc6b02486a5254103800d1, f6b3e3848a5fca63438984acd6d9eceac80814c1, e35acd56f244d94355f9ab237c2ecc8fba5e6f04 +3

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Sep 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 30 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.
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.

ghsa-6j38-2pg6-m9mv

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < fd63409b669f9951f1cc6b02486a5254103800d1	Fixed in fd63409b669f9951f1cc6b02486a5254103800d1
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < f6b3e3848a5fca63438984acd6d9eceac80814c1	Fixed in f6b3e3848a5fca63438984acd6d9eceac80814c1
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < e35acd56f244d94355f9ab237c2ecc8fba5e6f04	Fixed in e35acd56f244d94355f9ab237c2ecc8fba5e6f04
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < d16dac3925be95ad46e986d4b139c9898b6e227f	Fixed in d16dac3925be95ad46e986d4b139c9898b6e227f
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < cf398f67d9caa71af3b9fb9319058b22fe6b524e	Fixed in cf398f67d9caa71af3b9fb9319058b22fe6b524e
LinuxLinux	Affected ≥ afe4fd062416b158a8a8538b23adc1930a9b88dc, < 709f34f7c28dc4dd6c40343d101850f11e172312	Fixed in 709f34f7c28dc4dd6c40343d101850f11e172312

AI-suggested

The vulnerability has been resolved by clamping psched_mtu() to a safe range before multiplication and capping the quantum values to prevent overflow. Users should apply the official Linux kernel updates that include this fix. No additional mitigation is indicated beyond applying the patch.

Description

A vulnerability in the Linux kernel's fq (Fair Queueing) scheduler allows an attacker with CAP_NET_ADMIN privileges to cause a soft lockup by exploiting integer overflow in quantum calculations. This occurs when a device has an unusually large MTU, causing multiplication overflow and resulting in an infinite loop under the qdisc lock.

Impact

An attacker with CAP_NET_ADMIN privileges in a user namespace can configure a device with a large MTU to trigger an integer overflow in the fq scheduler, causing a soft lockup (system hang) due to an infinite loop under the qdisc lock. This results in denial of service on the affected system.

Summary

The Linux kernel's fq_init() function calculates quantum and initial_quantum values by multiplying psched_mtu() by 2 and 10 respectively, without checking for integer overflow. On devices with very large MTU values (e.g., a dummy device accepting MTU 2147483634), these multiplications wrap around to zero in 32-bit arithmetic, causing q->quantum to be zero. This leads to an infinite loop in fq_dequeue() where the credit-refill loop never progresses, causing a soft lockup under the qdisc lock. The fix clamps psched_mtu() to a range [1, 1 << 20] before multiplication and caps the result at 1 << 20, preventing overflow and matching existing bounds.

References

Community reviews

Loading reviews…