# CVE-2026-90099: linux: In the Linux kernel, the following vulnerability has been resolved:  net/sched: account classifier filter allocations...

CVE-2026-90099 is fixed in linux on 1 platform, first by DEBIAN-CVE-2026-90099, released September 23, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-90099
- Priority: Routine
- CVSS: n/a
- EPSS: 0.0022
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Sep 17, 2026

## Description

In the Linux kernel, the following vulnerability has been resolved:  net/sched: account classifier filter allocations to memcg  Allocations in the tc classifier *_change() paths (filter objects, per-CPU counters, and per-filter aux data) use plain GFP_KERNEL without __GFP_ACCOUNT, allowing unprivileged users to pin kernel memory outside memcg charging. The shared tcf_exts_init_ex() action array allocation in cls_api.c was also uncharged; this patch closes it along with the per-classifier filter-object/percpu/aux allocations that remain unaccounted.  Add GFP_KERNEL_ACCOUNT to: - the shared tcf_exts_init_ex() action array (cls_api.c), common to every   filter of every classifier (32 pointers, 256 bytes); - the filter-object, per-CPU-counter, and per-filter aux allocations in   cls_basic, cls_bpf, cls_cgroup, cls_flow, cls_flower, cls_fw,   cls_matchall, cls_route and cls_u32; - the u32_init_knode() replace-path knode allocation (cls_u32.c), which   allocates the same struct tc_u_knode + sel.keys on every replace of an   existing knode and was missed by the create-path-only conversion.  Also fix the cls_basic error path: basic_change() inserts fnew into the IDR before allocating the per-CPU counter. If alloc_percpu() fails the errout path kfree'd fnew without idr_remove, leaving a dangling pointer in the IDR. With GFP_KERNEL_ACCOUNT the percpu alloc becomes failable on demand (memcg at memory.max), making the dead path attacker-reachable and burning the handle permanently. Add the idr_remove on the percpu failure path, matching the basic_set_parms failure-path pattern.  Note: vega@nebusec.ai provided a poc for basic_cls, but it was easy to extend to the other classifiers.  Conditions to recreate the bug: - CONFIG_NET_SCHED, CONFIG_NET_CLS_* (the classifier being used),   CONFIG_NET_CLS_ACT, CONFIG_MEMCG, CONFIG_USER_NS, CONFIG_NET_NS. - Unprivileged user in a fresh user+network namespace (unshare -Urn),   or root with CAP_NET_ADMIN. - Create a large number of tc filters (e.g. tc filter add dev lo   ingress ... <classifier> ...) while watching a memcg-limited cgroup:   system slab grows far faster than memory.current, pinning kernel   memory outside memcg charging.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | linux Debian 13.5 (trixie) | 6.12.115-2 | [DEBIAN-CVE-2026-90099](https://patchblox.com/security/data/fix/linux/debian-cve-2026-90099.md) | Sep 23, 2026 |
| Linux | linux Debian 14 | 7.2.6-1 | [DEBIAN-CVE-2026-90099](https://patchblox.com/security/data/fix/linux/debian-cve-2026-90099.md) | Sep 23, 2026 |

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Data as of 2026-11-08T13:06:02Z 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

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