CVE-2025-38193 (GCVE-0-2025-38193)
Vulnerability from cvelistv5
Published
2025-07-04 13:37
Modified
2026-08-05 12:00
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: sch_sfq: reject invalid perturb period Gerrard Tai reported that SFQ perturb_period has no range check yet, and this can be used to trigger a race condition fixed in a separate patch. We want to make sure ctl->perturb_period * HZ will not overflow and is positive. tc qd add dev lo root sfq perturb -10 # negative value : error Error: sch_sfq: invalid perturb period. tc qd add dev lo root sfq perturb 1000000000 # too big : error Error: sch_sfq: invalid perturb period. tc qd add dev lo root sfq perturb 2000000 # acceptable value tc -s -d qd sh dev lo qdisc sfq 8005: root refcnt 2 limit 127p quantum 64Kb depth 127 flows 128 divisor 1024 perturb 2000000sec Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0) backlog 0b 0p requeues 0
References
Impacted products
Vendor Product Version
Linux Linux Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
Version: 1da177e4c3f41524e886b7f1b8a0c1fc7321cac2
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          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet_sched: sch_sfq: reject invalid perturb period\n\nGerrard Tai reported that SFQ perturb_period has no range check yet,\nand this can be used to trigger a race condition fixed in a separate patch.\n\nWe want to make sure ctl-\u003eperturb_period * HZ will not overflow\nand is positive.\n\n\ntc qd add dev lo root sfq perturb -10   # negative value : error\nError: sch_sfq: invalid perturb period.\n\ntc qd add dev lo root sfq perturb 1000000000 # too big : error\nError: sch_sfq: invalid perturb period.\n\ntc qd add dev lo root sfq perturb 2000000 # acceptable value\ntc -s -d qd sh dev lo\nqdisc sfq 8005: root refcnt 2 limit 127p quantum 64Kb depth 127 flows 128 divisor 1024 perturb 2000000sec\n Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)\n backlog 0b 0p requeues 0"
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            "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
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              "value": "AV:L - The attacker-controlled `perturb_period` arrives via an RTM_NEWQDISC netlink message on an AF_NETLINK socket (tc qdisc add/change), which requires local system access. No remote peer or packet data can influence this value.\nAC:L - A single deterministic command (`tc qdisc add dev lo root sfq perturb -10`, or a value that overflows `* HZ`) sets the malicious period every time, with no reliance on conditions outside the attacker\u0027s control; for the downstream qdisc race, this bug is itself the mechanism that makes the timing attacker-controlled and the race reliably winnable.\nPR:L - The path is gated only by `netlink_net_capable(skb, CAP_NET_ADMIN)`, evaluated against the netns owner\u0027s user namespace, so any unprivileged user obtains it with `unshare -Urn` and then configures SFQ on lo/veth. `sch_sfq` is loaded on demand via module alias, so no real root in the initial namespace is required.\nUI:N - The attacker performs the entire sequence \u2014 create the namespace, add the SFQ qdisc with the invalid period, and drive the parent qdisc change \u2014 with no action by any other user.\nS:U - The corrupted state (SFQ timer state, parent qdisc qlen/backlog accounting, and resulting freed qdisc objects) all lives within the kernel\u0027s own security authority; this is standard kernel-local escalation, not a VM, IOMMU, or hypervisor boundary crossing.\nC:H - By making the SFQ perturb timer fire at an attacker-chosen instant, this bug enables the parent-qdisc qlen/backlog underflow that yields a use-after-free of qdisc objects, giving an attacker-controllable read primitive over reclaimed kernel memory and disclosure of arbitrary kernel data.\nI:H - The same underflow-driven use-after-free permits heap spraying over the freed qdisc allocation and attacker-controlled writes into kernel structures (including function pointers in Qdisc_ops paths), which is the documented route to full privilege escalation for this class of net/sched bug.\nA:H - A negative period makes `mod_timer(jiffies + period)` expire in the past, so `sfq_perturbation()` re-arms and re-fires every tick forever, holding the root qdisc lock while rehashing every queued packet across up to 65408 flows \u2014 a permanent softirq livelock that stalls the device\u0027s transmit path, and the resulting UAF crashes the kernel outright."
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    "dateUpdated": "2026-08-05T12:00:18.140Z",
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