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CVE-2026-74506 (GCVE-0-2026-74506)

Vulnerability from cvelistv5 – Published: 2026-08-15 12:27 – Updated: 2026-08-17 05:47
VLAI
Title
afs: Fix UAF when sending a message
Summary
In the Linux kernel, the following vulnerability has been resolved: afs: Fix UAF when sending a message In afs_make_call(), there's a race with async call reception and destruction. If a call is dispatched that doesn't have call->write_iter set (used to specify the data content for FS.StoreData), then the first rxrpc_kernel_send_data() will not set MSG_MORE in the msghdr. Once rxrpc_send_data() queues the last request packet, the response could come in at any time and cause the call to be completed and put. However, afs_make_call() will look at the call again to see it ->write_iter should be handled - something it's only allowed to do if it has its own ref on the call. Whilst this is the case for synchronous calls, it isn't true for async calls such as FS.FetchData. There's also a potential UAF in afs_make_call() in the event that an asynchronous call is being sent, but the call fails in some way (e.g. it gets aborted from the server). The problem there is that afs_make_call() tries to abort a call if the rxrpc send fails, but the asynchronous notification from rxrpc may have caused the afs_call to be torn down. generic/650 plays games with randomly taking CPUs offline, and can interject a significant delay such that the call is deallocated before afs_make_call() gets to check call->write_iter - and a UAF ensues (caught by KASAN). BUG: KASAN: slab-use-after-free in afs_make_call+0x1c90/0x2210 [kafs] Read of size 8 at addr ffff888035e050e8 by task fsstress/1409 Fix this by making afs_make_op_call() give the op->call its own ref rather than transferring the caller's ref to it and then dropping the ref when afs_make_call() returns. This also means that the afs_make_call() func never loses its ref on the call now.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2 , < c0d3b81f703b2a9e37fe1347610a50cdf0078c27 (git)
Affected: e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2 , < daaa726b14fc3026a6b328614d312b698f62f391 (git)
Affected: e49c7b2f6de7ff81ca34c56e4eeb4fa740c099f2 , < 4af1ec68d54b3871155914d584fb10669c41a861 (git)
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Linux Linux Affected: 5.8
Unaffected: 0 , < 5.8 (semver)
Unaffected: 6.18.44 , ≤ 6.18.* (semver)
Unaffected: 7.1.8 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
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{
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              "value": "AV:L - The UAF is in kAFS client afs_make_call() during outbound FS.FetchData/YFS.FetchData RPCs, reached via local VFS read or readahead on an afs-mounted file (read_iter \u2192 afs_issue_read \u2192 afs_fs_fetch_data \u2192 afs_make_op_call), not from unsolicited remote packet processing alone.\nAC:L - The attacker controls both sides of the race: concurrent reads/readahead (as in xfstests generic/650 fsstress) while a fast or malicious AFS server reply completes and frees the async afs_call before afs_make_call() re-checks call-\u003ewrite_iter; no uncontrolled memory layout is required.\nPR:L - Any unprivileged local user with read permission on an already-mounted AFS volume can trigger async FetchData; mounting requires admin, but exercising the vulnerable read path needs only normal file access, matching the unprivileged fsstress reproducer.\nUI:N - No victim interaction is required; the attacker or local stress tool initiates the reads that dispatch the vulnerable async RPC, and AFS being mounted is an environmental precondition rather than interactive user action.\nS:U - The slab use-after-free in the kernel AFS client may enable local privilege escalation but does not cross a VM, container runtime, or IOMMU security boundary.\nC:H - KASAN reports slab-use-after-free with an 8-byte read of call-\u003ewrite_iter after async completion frees the afs_call; UAF over attacker-influenceable freed slab memory enables arbitrary kernel memory read primitives.\nI:H - The same use-after-free in afs_make_call() can be leveraged via heap grooming and spraying to obtain arbitrary kernel write or control-flow hijack, not merely a benign crash.\nA:H - The bug reliably triggers KASAN failures and kernel oops during normal async FetchData I/O, and UAF races can panic or wedge the system even before full exploit development."
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      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: afs: Fix UAF when sending a message",
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}



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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.


Detection rules are retrieved from Rulezet.