Linux: Use After Free
CVE-2024-40927 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 26460c1afa311524f588e288a4941432f0de6228, 633f72cb6124ecda97b641fbc119340bd88d51a9, 949be4ec5835e0ccb3e2a8ab0e46179cb5512518 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 0.29% 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 26460c1afa311524f588e288a4941432f0de6228 or 633f72cb6124ecda97b641fbc119340bd88d51a9 or 949be4ec5835e0ccb3e2a8ab0e46179cb5512518 or 61593dc413c3655e4328a351555235bc3089486a, whichever matches your release line, or a later version.
- Update Linux Kernel to 5.15.162 or 6.1.95 or 6.6.35 or 6.9.6, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | e9df17eb1408cfafa3d1844bfc7f22c7237b31b8 up to, but not including, 26460c1afa311524f588e288a4941432f0de6228; e9df17eb1408cfafa3d1844bfc7f22c7237b31b8 up to, but not including, 633f72cb6124ecda97b641fbc119340bd88d51a9; e9df17eb1408cfafa3d1844bfc7f22c7237b31b8 up to, but not including, 949be4ec5835e0ccb3e2a8ab0e46179cb5512518; e9df17eb1408cfafa3d1844bfc7f22c7237b31b8 up to, but not including, 61593dc413c3655e4328a351555235bc3089486a; e9df17eb1408cfafa3d1844bfc7f22c7237b31b8 up to, but not including, 5ceac4402f5d975e5a01c806438eb4e554771577; 2.6.35 | 26460c1afa311524f588e288a4941432f0de6228, 633f72cb6124ecda97b641fbc119340bd88d51a9, 949be4ec5835e0ccb3e2a8ab0e46179cb5512518, 61593dc413c3655e4328a351555235bc3089486a, 5ceac4402f5d975e5a01c806438eb4e554771577 |
| Linux | Linux Kernel | 2.6.35 up to, but not including, 5.15.162; 5.16 up to, but not including, 6.1.95; 6.2 up to, but not including, 6.6.35; 6.7 up to, but not including, 6.9.6; 6.10 | 5.15.162, 6.1.95, 6.6.35, 6.9.6 |
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 NVD.
Official description
In the Linux kernel, the following vulnerability has been resolved: xhci: Handle TD clearing for multiple streams case When multiple streams are in use, multiple TDs might be in flight when an endpoint is stopped. We need to issue a Set TR Dequeue Pointer for each, to ensure everything is reset properly and the caches cleared. Change the logic so that any N>1 TDs found active for different streams are deferred until after the first one is processed, calling xhci_invalidate_cancelled_tds() again from xhci_handle_cmd_set_deq() to queue another command until we are done with all of them. Also change the error/"should never happen" paths to ensure we at least clear any affected TDs, even if we can't issue a command to clear the hardware cache, and complain loudly with an xhci_warn() if this ever happens. This problem case dates back to commit e9df17eb1408 ("USB: xhci: Correct assumptions about number of rings per endpoint.") early on in the XHCI driver's life, when stream support was first added. It was then identified but not fixed nor made into a warning in commit 674f8438c121 ("xhci: split handling halted endpoints into two steps"), which added a FIXME comment for the problem case (without materially changing the behavior as far as I can tell, though the new logic made the problem more obvious). Then later, in commit 94f339147fc3 ("xhci: Fix failure to give back some cached cancelled URBs."), it was acknowledged again. [Mathias: commit 94f339147fc3 ("xhci: Fix failure to give back some cached cancelled URBs.") was a targeted regression fix to the previously mentioned patch. Users reported issues with usb stuck after unmounting/disconnecting UAS devices. This rolled back the TD clearing of multiple streams to its original state.] Apparently the commit author was aware of the problem (yet still chose to submit it): It was still mentioned as a FIXME, an xhci_dbg() was added to log the problem condition, and the remaining issue was mentioned in the commit description. The choice of making the log type xhci_dbg() for what is, at this point, a completely unhandled and known broken condition is puzzling and unfortunate, as it guarantees that no actual users would see the log in production, thereby making it nigh undebuggable (indeed, even if you turn on DEBUG, the message doesn't really hint at there being a problem at all). It took me *months* of random xHC crashes to finally find a reliable repro and be able to do a deep dive debug session, which could all have been avoided had this unhandled, broken condition been actually reported with a warning, as it should have been as a bug intentionally left in unfixed (never mind that it shouldn't have been left in at all). > Another fix to solve clearing the caches of all stream rings with > cancelled TDs is needed, but not as urgent. 3 years after that statement and 14 years after the original bug was introduced, I think it's finally time to fix it. And maybe next time let's not leave bugs unfixed (that are actually worse than the original bug), and let's actually get people to review kernel commits please. Fixes xHC crashes and IOMMU faults with UAS devices when handling errors/faults. Easiest repro is to use `hdparm` to mark an early sector (e.g. 1024) on a disk as bad, then `cat /dev/sdX > /dev/null` in a loop. At least in the case of JMicron controllers, the read errors end up having to cancel two TDs (for two queued requests to different streams) and the one that didn't get cleared properly ends up faulting the xHC entirely when it tries to access DMA pages that have since been unmapped, referred to by the stale TDs. This normally happens quickly (after two or three loops). After this fix, I left the `cat` in a loop running overnight and experienced no xHC failures, with all read errors recovered properly. Repro'd and tested on an Apple M1 Mac Mini (dwc3 host). On systems without an IOMMU, this bug would instead silently corrupt freed memory, making this a ---truncated---
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: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/26460c1afa311524f588e288a4941432f0de6228
- git.kernel.org/stable/c/5ceac4402f5d975e5a01c806438eb4e554771577
- git.kernel.org/stable/c/61593dc413c3655e4328a351555235bc3089486a
- git.kernel.org/stable/c/633f72cb6124ecda97b641fbc119340bd88d51a9
- git.kernel.org/stable/c/949be4ec5835e0ccb3e2a8ab0e46179cb5512518
Other references
Recent Use After Free vulnerabilities
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