CVE-2025-38107 (GCVE-0-2025-38107)
Vulnerability from cvelistv5
Published
2025-07-03 08:35
Modified
2026-08-05 11:59
Severity ?
7.8 (High) - CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: net_sched: ets: fix a race in ets_qdisc_change() Gerrard Tai reported a race condition in ETS, whenever SFQ perturb timer fires at the wrong time. The race is as follows: CPU 0 CPU 1 [1]: lock root [2]: qdisc_tree_flush_backlog() [3]: unlock root | | [5]: lock root | [6]: rehash | [7]: qdisc_tree_reduce_backlog() | [4]: qdisc_put() This can be abused to underflow a parent's qlen. Calling qdisc_purge_queue() instead of qdisc_tree_flush_backlog() should fix the race, because all packets will be purged from the qdisc before releasing the lock.
References
Impacted products
Vendor Product Version
Linux Linux Version: 699d82e9a6db29d509a71f1f2f4316231e6232e6
Version: ce881ddbdc028fb1988b66e40e45ca0529c23b46
Version: b05972f01e7d30419987a1f221b5593668fd6448
Version: b05972f01e7d30419987a1f221b5593668fd6448
Version: b05972f01e7d30419987a1f221b5593668fd6448
Version: b05972f01e7d30419987a1f221b5593668fd6448
Version: b05972f01e7d30419987a1f221b5593668fd6448
Version: fffa19b5e58c34004a0d6f642d9c24b11d213994
Version: fb155f6597cd7bc3aeed668c3bb15fc3b7cb257d
Version: 5.10.142   ≤
Version: 5.15.66   ≤
Version: 5.4.213   ≤
Version: 5.19.8   ≤
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: ets: fix a race in ets_qdisc_change()\n\nGerrard Tai reported a race condition in ETS, whenever SFQ perturb timer\nfires at the wrong time.\n\nThe race is as follows:\n\nCPU 0                                 CPU 1\n[1]: lock root\n[2]: qdisc_tree_flush_backlog()\n[3]: unlock root\n |\n |                                    [5]: lock root\n |                                    [6]: rehash\n |                                    [7]: qdisc_tree_reduce_backlog()\n |\n[4]: qdisc_put()\n\nThis can be abused to underflow a parent\u0027s qlen.\n\nCalling qdisc_purge_queue() instead of qdisc_tree_flush_backlog()\nshould fix the race, because all packets will be purged from the qdisc\nbefore releasing the lock."
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              "value": "AV:L - The vulnerable code is reached only through `RTM_NEWQDISC` netlink messages (`tc qdisc change ... ets bands N`) plus locally enqueued packets, requiring local system access. No remote peer input reaches `ets_qdisc_change()`.\nAC:L - The attacker controls both sides of the race \u2014 they configure the SFQ child\u0027s `perturb` period, choose when to issue the band-shrinking `tc` change, and can retry the sequence unboundedly until the timer lands in the unlocked window between `sch_tree_unlock()` and `qdisc_put()`.\nPR:L - The tc/qdisc netlink path is gated only by `netlink_net_capable(skb, CAP_NET_ADMIN)` against the netns\u0027 own user namespace, so an unprivileged user obtains it via `unshare -Urn` and can also autoload `sch_ets`/`sch_sfq` from that context.\nUI:N - The attacker performs every step \u2014 creating the qdisc hierarchy, generating traffic, and triggering the change \u2014 entirely on their own. No victim action is involved.\nS:U - The corrupted `qlen`/`backlog` accounting and any resulting memory corruption are confined to the kernel\u0027s own security authority; this is standard local kernel privilege escalation with no VM, IOMMU, or sandbox boundary crossed.\nC:H - The double-subtraction underflows an unsigned `q.qlen`, desynchronizing the qdisc tree so classes remain on active lists after their child qdiscs are freed, yielding a use-after-free on `struct Qdisc`/class objects that can be groomed into an arbitrary kernel-memory read.\nI:H - The same qlen-desync-to-UAF primitive gives control over reallocated heap objects and their function pointers/list heads, enabling arbitrary write and control-flow hijacking \u2014 the well-known net/sched local privilege escalation pattern.\nA:H - Even unweaponized, the underflowed `qlen` makes an empty qdisc appear to hold ~4 billion packets, causing dequeue-from-empty warnings, stuck transmit paths, and use-after-free oopses that panic the kernel."
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          "url": "https://git.kernel.org/stable/c/0b479d0aa488cb478eb2e1d8868be946ac8afb4f"
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    "dateUpdated": "2026-08-05T11:59:35.210Z",
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