# CVE-2026-98427: net/sched: codel: bound the dropping loop per dequeue call

CVE-2026-98427 is fixed in linux on 1 platform by DEBIAN-CVE-2026-98427 (version 7.2.8-1), released October 16, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-98427
- Priority: Routine
- CVSS: 5.5 (Moderate)
- EPSS: 0.0020
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Oct 14, 2026
- Vendor advisory: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-98427

## Description

In the Linux kernel, the following vulnerability has been resolved:  net/sched: codel: bound the dropping loop per dequeue call  The CoDel control law schedules the next drop one interval/sqrt(count) after the previous drop, using the configured interval (codel_params.interval). For very small intervals the scheduled step rounds down to zero, so the dropping loop in codel_dequeue() never advances and drains the entire backlog under the qdisc lock in one call - an unprivileged user can trigger a soft lockup this way.  Fix in the shared codel code used by both codel and fq_codel:  1. Make the control-law step at least 1 tick so the dropping loop    always moves forward.  2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops    per codel_dequeue() call, resyncing drop_next to now when the cap    is hit: the catch-up owed to the loop grows with the idle gap and    the backlog, which no interval threshold can bound. This is a    deliberate behaviour change after long idle gaps.  The cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path (fixed interval, cap only).  The target sojourn delay (codel_params.target) is not validated: it does not feed the control law, so a sub-tick value is aggressive rather than deadlock-prone.  Conditions to recreate the bug:   - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000   - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel)   - unpatched kernel: tc accepts it; a UDP flood under the 1kbit tbf     soft-lockups (watchdog: BUG: soft lockup) while one     codel_dequeue() call drops the backlog under the qdisc lock   - patched kernel: same setup, at most 256 drops per dequeue call,     no soft lockup  Testing: claim reproducer and interval 2us/3us variants run clean; tdc qdisc category passes (see the selftests patch).

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 14 | 7.2.8-1 | [DEBIAN-CVE-2026-98427](https://patchblox.com/security/data/fix/linux/debian-cve-2026-98427.md) | Oct 16, 2026 |

---

Data as of 2026-11-09T01:18:40Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

Free to use with attribution: show "Data: Patchblox Patch Radar" with a link to https://patchblox.com/security/patch-radar. Terms, including what needs a written agreement: https://patchblox.com/security/patch-radar/use-the-data

Product names, logos and trademarks shown on Patch Radar belong to their respective owners. They are used only to identify the software each security fix applies to and to help readers find their platform. Their use does not imply any affiliation with, or endorsement by, those owners, and Patchblox is not affiliated with any of them.