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High severity7.8NVD Advisory· Published Nov 19, 2024· Updated May 12, 2026

CVE-2024-53057

CVE-2024-53057

Description

In the Linux kernel, the following vulnerability has been resolved:

net/sched: stop qdisc_tree_reduce_backlog on TC_H_ROOT

In qdisc_tree_reduce_backlog, Qdiscs with major handle ffff: are assumed to be either root or ingress. This assumption is bogus since it's valid to create egress qdiscs with major handle ffff: Budimir Markovic found that for qdiscs like DRR that maintain an active class list, it will cause a UAF with a dangling class pointer.

In 066a3b5b2346, the concern was to avoid iterating over the ingress qdisc since its parent is itself. The proper fix is to stop when parent TC_H_ROOT is reached because the only way to retrieve ingress is when a hierarchy which does not contain a ffff: major handle call into qdisc_lookup with TC_H_MAJ(TC_H_ROOT).

In the scenario where major ffff: is an egress qdisc in any of the tree levels, the updates will also propagate to TC_H_ROOT, which then the iteration must stop.

net/sched/sch_api.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A use-after-free vulnerability in Linux kernel's net/sched qdisc_tree_reduce_backlog occurs when egress qdiscs with major handle ffff: are created, leading to a dangling class pointer.

In the Linux kernel's net/sched subsystem, the qdisc_tree_reduce_backlog function incorrectly assumed that Qdiscs with major handle ffff: are either root or ingress. However, it is valid to create egress qdiscs with that handle, leading to a use-after-free (UAF) vulnerability when a qdisc like DRR that maintains an active class list is involved. The flaw was discovered by Budimir Markovic and stems from a bogus assumption in commit 066a3b5b2346, which aimed to avoid iterating over ingress qdiscs but failed to stop at TC_H_ROOT.

Exploitation requires local access and the ability to create network qdiscs. An attacker can craft a specific qdisc hierarchy that triggers the UAF by causing the function to continue past TC_H_ROOT, resulting in a dangling class pointer. No special privileges beyond those needed to configure qdiscs are necessary.

The impact is a potential kernel crash or, in worst-case scenarios, privilege escalation via the use-after-free condition. The vulnerability affects Linux kernel versions before the fix was applied.

Mitigation is available via the Linux kernel stable tree. The fix is commit dbe778b08b51, which stops the iteration when parent TC_H_ROOT is reached [4]. Users should update their kernels to a version containing this commit.

References
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AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

212

Patches

0

No patches discovered yet.

Vulnerability mechanics

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References

13

News mentions

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