CVE-2026-31607: Linux kernel · usbip: validate number_of_packets in usbip_pack_ret_submit()
Affects Linux kernelSource CVE Database V5
Not known to be exploited · CVSS 9.8 Critical · fixed in ef8ebb1c637b4cfb61a9dd2e013376774ee2033b : patch Linux kernel as a priority.
Data as of 26 Oct 2026, 10:24 UTC
- EPSS
- 0.3% chance of exploitation in 30 days – higher than 23% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
- CISA SSVC
- Exploitation
- No evidence of active exploitation and no public proof of concept
- Automatable
- Attackers can reliably automate steps 1–4 of the kill chain
- Technical impact
- Total control over the software or total information disclosure
CISA SSVC assessment, 2026-10-16.
- Patch
- Available – fixed in ef8ebb1c637b4cfb61a9dd2e013376774ee2033b, ce744264b06b97069b3722511ab355738311fee0, 324262c38438255bf6bdbf6342ca47c0badaab76 +11
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 24 Apr 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Upgrade to a fixed release listed under Affected software.
Affected software
| Product | Affected | Fixed in |
|---|---|---|
| LinuxLinux | Affected
| Fixed in
|
| LinuxLinux | Affected
| Fixed in– |
Description
In the Linux kernel, the following vulnerability has been resolved: usbip: validate number_of_packets in usbip_pack_ret_submit() When a USB/IP client receives a RET_SUBMIT response, usbip_pack_ret_submit() unconditionally overwrites urb->number_of_packets from the network PDU. This value is subsequently used as the loop bound in usbip_recv_iso() and usbip_pad_iso() to iterate over urb->iso_frame_desc[], a flexible array whose size was fixed at URB allocation time based on the *original* number_of_packets from the CMD_SUBMIT. A malicious USB/IP server can set number_of_packets in the response to a value larger than what was originally submitted, causing a heap out-of-bounds write when usbip_recv_iso() writes to urb->iso_frame_desc[i] beyond the allocated region. KASAN confirmed this with kernel 7.0.0-rc5: BUG: KASAN: slab-out-of-bounds in usbip_recv_iso+0x46a/0x640 Write of size 4 at addr ffff888106351d40 by task vhci_rx/69 The buggy address is located 0 bytes to the right of allocated 320-byte region [ffff888106351c00, ffff888106351d40) The server side (stub_rx.c) and gadget side (vudc_rx.c) already validate number_of_packets in the CMD_SUBMIT path since commits c6688ef9f297 ("usbip: fix stub_rx: harden CMD_SUBMIT path to handle malicious input") and b78d830f0049 ("usbip: fix vudc_rx: harden CMD_SUBMIT path to handle malicious input"). The server side validates against USBIP_MAX_ISO_PACKETS because no URB exists yet at that point. On the client side we have the original URB, so we can use the tighter bound: the response must not exceed the original number_of_packets. This mirrors the existing validation of actual_length against transfer_buffer_length in usbip_recv_xbuff(), which checks the response value against the original allocation size. Kelvin Mbogo's series ("usb: usbip: fix integer overflow in usbip_recv_iso()", v2) hardens the receive-side functions themselves; this patch complements that work by catching the bad value at its source -- in usbip_pack_ret_submit() before the overwrite -- and using the tighter per-URB allocation bound rather than the global USBIP_MAX_ISO_PACKETS limit. Fix this by checking rpdu->number_of_packets against urb->number_of_packets in usbip_pack_ret_submit() before the overwrite. On violation, clamp to zero so that usbip_recv_iso() and usbip_pad_iso() safely return early.
References
- git.kernel.org/stable/c/324262c38438255bf6bdbf6342ca47c0badaab76 (opens in a new tab)
- git.kernel.org/stable/c/973f2c250289f5bf6cc146b98aa6fdde11fe50d6 (opens in a new tab)
- git.kernel.org/stable/c/ce744264b06b97069b3722511ab355738311fee0 (opens in a new tab)
- git.kernel.org/stable/c/885c8591784da6314f9aa82fa460ac69f9f79e5f (opens in a new tab)
- git.kernel.org/stable/c/8d155e2d1c4102f74f82a2bf9c016164bb0f7384 (opens in a new tab)
- git.kernel.org/stable/c/906f16a836de13fe61f49cdce2f66f2dbd14caf4 (opens in a new tab)
- git.kernel.org/stable/c/ef8ebb1c637b4cfb61a9dd2e013376774ee2033b (opens in a new tab)
- git.kernel.org/stable/c/5e1c4ece08ccdc197177631f111845a2c68eede3 (opens in a new tab)
- git.kernel.org/stable/c/2ab833a16a825373aad2ba7d54b572b277e95b71 (opens in a new tab)
- access.redhat.com/security/cve/CVE-2026-31607 (opens in a new tab)
- bugzilla.redhat.com/show_bug.cgi?id=2461521 (opens in a new tab)
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-31607.json (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:25095 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:41236 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:24343 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:19569 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:23224 (opens in a new tab)
- access.redhat.com/errata/RHSA-2026:19568 (opens in a new tab)