CVE-2026-98427
net/sched: codel: bound the dropping loop per dequeue call
No known exploitation. EPSS puts it in the 9th percentile. Fixed versions are out.
What to do
Find your product and version, then upgrade to the build on the right.
- LinuxAffected: ≥ 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, < bacd72289d34d8c05b7de5a12448b87b6dd93878Upgrade to: bacd72289d34d8c05b7de5a12448b87b6dd93878Affected: ≥ 76e3cc126bb223013a6b9a0e2a51238d1ef2e409, < 7f4a5ec6258fd7c92633ec4b0493fc51166d9398Upgrade to: 7f4a5ec6258fd7c92633ec4b0493fc51166d9398Stated by: CVE record
Versions as the sources state them. Full version matrix after sign-in
What it is
From the CVE record
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).
In plain language
No plain-language summary for this CVE yet.
Exploitation
Where each signal puts this CVE on the scale from published to confirmed exploited.
- CISA KEV
Not in the catalog. CISA has not confirmed exploitation.
- Public exploits
No public exploit or proof of concept found in the sources we track.
- EPSS
0.2% chance of exploitation activity in the next 30 days, which ranks it in the 9th percentile of scored CVEs.
Exploit Prediction Scoring System, FIRST.org. A probability, not a confirmation.
Lifecycle
4 events over 8 days, from the signal feeds we watch.
- OpenVAS check added
- Record updated
- Publishedrecord updated
Affected products
Sources
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