Linux: Use After Free
CVE-2025-68815 is a high-severity use after free vulnerability in Linux, with a CVSS 3.1 base score of 7.8 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions 58fdce6bc005e964f1dbc3ca716f5fe0f68839a2, 02783a37cb1c0a2bd9fcba4ff1b81e6e209c7d87, 8067db5c95aab9461d23117679338cd8869831fa as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.15% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to 58fdce6bc005e964f1dbc3ca716f5fe0f68839a2 or 02783a37cb1c0a2bd9fcba4ff1b81e6e209c7d87 or 8067db5c95aab9461d23117679338cd8869831fa or 2f125ebe47d6369e562f3cbd9b6227cff51eaf34, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | f517335a61ff8037b18ba1b0a002c1f82926a934 up to, but not including, 58fdce6bc005e964f1dbc3ca716f5fe0f68839a2; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, 02783a37cb1c0a2bd9fcba4ff1b81e6e209c7d87; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, 8067db5c95aab9461d23117679338cd8869831fa; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, 2f125ebe47d6369e562f3cbd9b6227cff51eaf34; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, cca2ed931b734fe48139bc6f020e47367346630f; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, 43d9a530c8c094d137159784e7c951c65f11ec6c; cd9b50adc6bb9ad3f7d244590a389522215865c4 up to, but not including, b1e125ae425aba9b45252e933ca8df52a843ec70; d05330672afe2e142ba97e63bd7c1faef76781bb; and 3 more ranges | 58fdce6bc005e964f1dbc3ca716f5fe0f68839a2, 02783a37cb1c0a2bd9fcba4ff1b81e6e209c7d87, 8067db5c95aab9461d23117679338cd8869831fa, 2f125ebe47d6369e562f3cbd9b6227cff51eaf34, cca2ed931b734fe48139bc6f020e47367346630f, 43d9a530c8c094d137159784e7c951c65f11ec6c |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: net/sched: ets: Remove drr class from the active list if it changes to strict Whenever a user issues an ets qdisc change command, transforming a drr class into a strict one, the ets code isn't checking whether that class was in the active list and removing it. This means that, if a user changes a strict class (which was in the active list) back to a drr one, that class will be added twice to the active list [1]. Doing so with the following commands: tc qdisc add dev lo root handle 1: ets bands 2 strict 1 tc qdisc add dev lo parent 1:2 handle 20: \ tbf rate 8bit burst 100b latency 1s tc filter add dev lo parent 1: basic classid 1:2 ping -c1 -W0.01 -s 56 127.0.0.1 tc qdisc change dev lo root handle 1: ets bands 2 strict 2 tc qdisc change dev lo root handle 1: ets bands 2 strict 1 ping -c1 -W0.01 -s 56 127.0.0.1 Will trigger the following splat with list debug turned on: [ 59.279014][ T365] ------------[ cut here ]------------ [ 59.279452][ T365] list_add double add: new=ffff88801d60e350, prev=ffff88801d60e350, next=ffff88801d60e2c0. [ 59.280153][ T365] WARNING: CPU: 3 PID: 365 at lib/list_debug.c:35 __list_add_valid_or_report+0x17f/0x220 [ 59.280860][ T365] Modules linked in: [ 59.281165][ T365] CPU: 3 UID: 0 PID: 365 Comm: tc Not tainted 6.18.0-rc7-00105-g7e9f13163c13-dirty #239 PREEMPT(voluntary) [ 59.281977][ T365] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011 [ 59.282391][ T365] RIP: 0010:__list_add_valid_or_report+0x17f/0x220 [ 59.282842][ T365] Code: 89 c6 e8 d4 b7 0d ff 90 0f 0b 90 90 31 c0 e9 31 ff ff ff 90 48 c7 c7 e0 a0 22 9f 48 89 f2 48 89 c1 4c 89 c6 e8 b2 b7 0d ff 90 <0f> 0b 90 90 31 c0 e9 0f ff ff ff 48 89 f7 48 89 44 24 10 4c 89 44 ... [ 59.288812][ T365] Call Trace: [ 59.289056][ T365] <TASK> [ 59.289224][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.289546][ T365] ets_qdisc_change+0xd2b/0x1e80 [ 59.289891][ T365] ? __lock_acquire+0x7e7/0x1be0 [ 59.290223][ T365] ? __pfx_ets_qdisc_change+0x10/0x10 [ 59.290546][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.290898][ T365] ? __mutex_trylock_common+0xda/0x240 [ 59.291228][ T365] ? __pfx___mutex_trylock_common+0x10/0x10 [ 59.291655][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.291993][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.292313][ T365] ? trace_contention_end+0xc8/0x110 [ 59.292656][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.293022][ T365] ? srso_alias_return_thunk+0x5/0xfbef5 [ 59.293351][ T365] tc_modify_qdisc+0x63a/0x1cf0 Fix this by always checking and removing an ets class from the active list when changing it to strict. [1] https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/tree/net/sched/sch_ets.c?id=ce052b9402e461a9aded599f5b47e76bc727f7de#n663
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
- git.kernel.org/stable/c/02783a37cb1c0a2bd9fcba4ff1b81e6e209c7d87
- git.kernel.org/stable/c/2f125ebe47d6369e562f3cbd9b6227cff51eaf34
- git.kernel.org/stable/c/43d9a530c8c094d137159784e7c951c65f11ec6c
- git.kernel.org/stable/c/58fdce6bc005e964f1dbc3ca716f5fe0f68839a2
- git.kernel.org/stable/c/8067db5c95aab9461d23117679338cd8869831fa
- git.kernel.org/stable/c/b1e125ae425aba9b45252e933ca8df52a843ec70
- git.kernel.org/stable/c/cca2ed931b734fe48139bc6f020e47367346630f
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