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10.0

CVE-2026-63795: Linux kernel 9p client may free file handle too early

CVE-2026-63795 · published 3 months ago
Summary

The Linux kernel's 9p network file system can accidentally delete a file handle that the program still needs if a multi-step walk operation fails. This can cause the program to crash or behave unexpectedly. Updating the kernel to the latest version resolves the issue.

What to do
  • Update linux kernel to version 7.1.3.
  • Update debian linux to version 6.1.177-1.
  • Update debian linux to version 6.12.95-1.
  • Update debian linux to version 7.1.3-1.
  • Update canonical linux-aws-7.0 to version 7.0.0-1012.12~24.04.1.
  • Update canonical linux-azure-7.0 to version 7.0.0-1014.14~24.04.1.
  • Update canonical linux-gcp-7.0 to version 7.0.0-1011.11~24.04.1.
  • Update canonical linux-hwe-7.0 to version 7.0.0-31.31~24.04.1.
  • Update canonical linux-nvidia-7.0 to version 7.0.0-1018.18~24.04.1.
  • Update canonical linux-nvidia-tegra to version 6.8.0-1035.38.
  • Update canonical linux-oracle-7.0 to version 7.0.0-1011.11~24.04.1.
  • Update canonical linux-riscv-7.0 to version 7.0.0-31.31.1~24.04.1.
  • Update canonical linux to version 7.0.0-31.31.
  • Update canonical linux-aws to version 7.0.0-1012.12.
  • Update canonical linux-azure to version 7.0.0-1014.14.
  • Update canonical linux-gcp to version 7.0.0-1011.11.
  • Update canonical linux-gke to version 7.0.0-1006.7.
  • Update canonical linux-ibm to version 7.0.0-1013.13.
  • Update canonical linux-nvidia to version 7.0.0-1018.18.
  • Update canonical linux-nvidia-bos to version 7.0.0-2018.18.
  • Update canonical linux-oem-7.0 to version 7.0.0-1013.13.
  • Update canonical linux-oracle to version 7.0.0-1011.11.
  • Update canonical linux-raspi to version 7.0.0-1019.19.
  • Update canonical linux-realtime to version 7.0.0-31.31.1.
  • Update canonical linux-riscv to version 7.0.0-31.31.1.
  • Update canonical linux to version 6.8.0-147.147.
  • Update canonical linux-aws to version 6.8.0-1067.70.
  • Update canonical linux-azure to version 6.8.0-1071.79.
  • Update canonical linux-azure-fde to version 6.8.0-1069.76.
  • Update canonical linux-azure-fde-7.0 to version 7.0.0-1013.13~24.04.1.
  • Update canonical linux-gcp to version 6.8.0-1071.79.
  • Update canonical linux-gke to version 6.8.0-1066.74.
  • Update canonical linux-gkeop to version 6.8.0-1052.56.
  • Update canonical linux-ibm to version 6.8.0-1067.68.
  • Update canonical linux-lowlatency to version 6.8.0-147.147.1.
  • Update canonical linux-oracle to version 6.8.0-1064.67.
  • Update canonical linux-bluefield to version 6.8.0-1033.38.
  • Update canonical linux-realtime to version 6.8.1-1062.63.
  • Update canonical linux-aws-fips to version 6.8.0-1067.70+fips1.
  • Update canonical linux-azure-fips to version 6.8.0-1071.79+fips1.
  • Update canonical linux-fips to version 6.8.0-147.147+fips1.
  • Update canonical linux-gcp-fips to version 6.8.0-1071.79+fips1.
  • Update canonical linux-azure-fde to version 7.0.0-1013.13.
  • Update linux linux to version 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 or later.
Affected software
Ecosystem VendorProductAffected versions
Linux linux kernel >= 6.19.0, < 7.1.3
Fix: upgrade to 7.1.3
– linux linux < 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070
6.0
Debian:12 debian linux < 6.1.177-1
Fix: upgrade to 6.1.177-1
Debian:13 debian linux < 6.12.95-1
Fix: upgrade to 6.12.95-1
Debian:14 debian linux < 7.1.3-1
Fix: upgrade to 7.1.3-1
– linux linux_kernel >= 6.0, < 6.1.177
>= 6.2, < 6.6.144
>= 6.7, < 6.12.95
>= 6.13, < 6.18.38
>= 6.19, < 7.1.3
cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
Ubuntu:16.04:LTS canonical linux-hwe-edge All versions
Ubuntu:18.04:LTS canonical linux-aws-5.0 All versions
Ubuntu:18.04:LTS canonical linux-aws-5.3 All versions
Ubuntu:18.04:LTS canonical linux-azure All versions
Ubuntu:18.04:LTS canonical linux-azure-5.3 All versions
Ubuntu:18.04:LTS canonical linux-azure-edge All versions
Ubuntu:18.04:LTS canonical linux-gcp All versions
Ubuntu:18.04:LTS canonical linux-gcp-5.3 All versions
Ubuntu:18.04:LTS canonical linux-gke-4.15 All versions
Ubuntu:18.04:LTS canonical linux-gke-5.4 All versions
Ubuntu:18.04:LTS canonical linux-gkeop-5.4 All versions
Ubuntu:18.04:LTS canonical linux-hwe All versions
Ubuntu:18.04:LTS canonical linux-oem All versions
Ubuntu:18.04:LTS canonical linux-oracle-5.0 All versions
Ubuntu:18.04:LTS canonical linux-oracle-5.3 All versions
Ubuntu:20.04:LTS canonical linux-aws-5.11 All versions
Ubuntu:20.04:LTS canonical linux-aws-5.13 All versions
Ubuntu:20.04:LTS canonical linux-aws-5.8 All versions
Ubuntu:20.04:LTS canonical linux-azure-5.11 All versions
Ubuntu:20.04:LTS canonical linux-azure-5.13 All versions
Ubuntu:20.04:LTS canonical linux-azure-5.8 All versions
Ubuntu:20.04:LTS canonical linux-azure-fde All versions
Ubuntu:20.04:LTS canonical linux-gcp-5.11 All versions
Ubuntu:20.04:LTS canonical linux-gcp-5.13 All versions
Ubuntu:20.04:LTS canonical linux-gcp-5.8 All versions
Ubuntu:20.04:LTS canonical linux-gke All versions
Ubuntu:20.04:LTS canonical linux-gke-5.15 All versions
Ubuntu:20.04:LTS canonical linux-gkeop All versions
Ubuntu:20.04:LTS canonical linux-gkeop-5.15 All versions
Ubuntu:20.04:LTS canonical linux-hwe-5.11 All versions
Ubuntu:20.04:LTS canonical linux-hwe-5.13 All versions
Ubuntu:20.04:LTS canonical linux-hwe-5.8 All versions
Ubuntu:20.04:LTS canonical linux-intel-5.13 All versions
Ubuntu:20.04:LTS canonical linux-oem-5.10 All versions
Ubuntu:20.04:LTS canonical linux-oem-5.13 All versions
Ubuntu:20.04:LTS canonical linux-oem-5.14 All versions
Ubuntu:20.04:LTS canonical linux-oem-5.6 All versions
Ubuntu:20.04:LTS canonical linux-oracle-5.11 All versions
Ubuntu:20.04:LTS canonical linux-oracle-5.13 All versions
Ubuntu:20.04:LTS canonical linux-oracle-5.8 All versions
Ubuntu:20.04:LTS canonical linux-raspi2 All versions
Ubuntu:20.04:LTS canonical linux-riscv All versions
Ubuntu:20.04:LTS canonical linux-riscv-5.11 All versions
Ubuntu:20.04:LTS canonical linux-riscv-5.8 All versions
Showing 50 of 165. Show the rest
Ecosystem VendorProductAffected versions
Ubuntu:22.04:LTS canonical linux-allwinner-5.19 All versions
Ubuntu:22.04:LTS canonical linux-aws-5.19 All versions
Ubuntu:22.04:LTS canonical linux-aws-6.2 All versions
Ubuntu:22.04:LTS canonical linux-aws-6.5 All versions
Ubuntu:22.04:LTS canonical linux-aws-6.8 All versions
Ubuntu:22.04:LTS canonical linux-azure-5.19 All versions
Ubuntu:22.04:LTS canonical linux-azure-6.2 All versions
Ubuntu:22.04:LTS canonical linux-azure-6.5 All versions
Ubuntu:22.04:LTS canonical linux-azure-6.8 All versions
Ubuntu:22.04:LTS canonical linux-azure-fde-5.19 All versions
Ubuntu:22.04:LTS canonical linux-azure-fde-6.2 All versions
Ubuntu:22.04:LTS canonical linux-azure-fde-6.8 All versions
Ubuntu:22.04:LTS canonical linux-gcp-5.19 All versions
Ubuntu:22.04:LTS canonical linux-gcp-6.2 All versions
Ubuntu:22.04:LTS canonical linux-gcp-6.5 All versions
Ubuntu:22.04:LTS canonical linux-gcp-6.8 All versions
Ubuntu:22.04:LTS canonical linux-hwe-5.19 All versions
Ubuntu:22.04:LTS canonical linux-hwe-6.2 All versions
Ubuntu:22.04:LTS canonical linux-hwe-6.5 All versions
Ubuntu:22.04:LTS canonical linux-hwe-6.8 All versions
Ubuntu:22.04:LTS canonical linux-ibm-6.8 All versions
Ubuntu:22.04:LTS canonical linux-intel-iot-realtime All versions
Ubuntu:22.04:LTS canonical linux-lowlatency-hwe-5.19 All versions
Ubuntu:22.04:LTS canonical linux-lowlatency-hwe-6.2 All versions
Ubuntu:22.04:LTS canonical linux-lowlatency-hwe-6.5 All versions
Ubuntu:22.04:LTS canonical linux-lowlatency-hwe-6.8 All versions
Ubuntu:22.04:LTS canonical linux-nvidia-6.2 All versions
Ubuntu:22.04:LTS canonical linux-nvidia-6.5 All versions
Ubuntu:22.04:LTS canonical linux-nvidia-6.8 All versions
Ubuntu:22.04:LTS canonical linux-oem-5.17 All versions
Ubuntu:22.04:LTS canonical linux-oem-6.0 All versions
Ubuntu:22.04:LTS canonical linux-oem-6.1 All versions
Ubuntu:22.04:LTS canonical linux-oem-6.5 All versions
Ubuntu:22.04:LTS canonical linux-oracle-6.5 All versions
Ubuntu:22.04:LTS canonical linux-oracle-6.8 All versions
Ubuntu:22.04:LTS canonical linux-realtime All versions
Ubuntu:22.04:LTS canonical linux-riscv-5.19 All versions
Ubuntu:22.04:LTS canonical linux-riscv-6.5 All versions
Ubuntu:22.04:LTS canonical linux-riscv-6.8 All versions
Ubuntu:22.04:LTS canonical linux-starfive-5.19 All versions
Ubuntu:22.04:LTS canonical linux-starfive-6.2 All versions
Ubuntu:22.04:LTS canonical linux-starfive-6.5 All versions
Ubuntu:Pro:Realtime:22.04:LTS canonical linux-realtime-6.8 All versions
Ubuntu:24.04:LTS canonical linux < 6.8.0-147.147
Fix: upgrade to 6.8.0-147.147
Ubuntu:24.04:LTS canonical linux-aws < 6.8.0-1067.70
Fix: upgrade to 6.8.0-1067.70
Ubuntu:24.04:LTS canonical linux-aws-6.14 All versions
Ubuntu:24.04:LTS canonical linux-aws-6.17 All versions
Ubuntu:24.04:LTS canonical linux-aws-7.0 < 7.0.0-1012.12~24.04.1
Fix: upgrade to 7.0.0-1012.12~24.04.1
Ubuntu:24.04:LTS canonical linux-azure-6.11 All versions
Ubuntu:24.04:LTS canonical linux-azure-6.14 All versions
Ubuntu:24.04:LTS canonical linux-azure-6.17 All versions
Ubuntu:24.04:LTS canonical linux-azure-7.0 < 7.0.0-1014.14~24.04.1
Fix: upgrade to 7.0.0-1014.14~24.04.1
Ubuntu:24.04:LTS canonical linux-azure-fde-6.14 All versions
Ubuntu:24.04:LTS canonical linux-azure-fde-6.17 All versions
Ubuntu:24.04:LTS canonical linux-azure-fde-7.0 < 7.0.0-1013.13~24.04.1
Fix: upgrade to 7.0.0-1013.13~24.04.1
Ubuntu:24.04:LTS canonical linux-azure-nvidia All versions
Ubuntu:24.04:LTS canonical linux-azure-nvidia-6.14 All versions
Ubuntu:24.04:LTS canonical linux-gcp-6.11 All versions
Ubuntu:24.04:LTS canonical linux-gcp-6.14 All versions
Ubuntu:24.04:LTS canonical linux-gcp-6.17 All versions
Ubuntu:24.04:LTS canonical linux-gcp-7.0 < 7.0.0-1011.11~24.04.1
Fix: upgrade to 7.0.0-1011.11~24.04.1
Ubuntu:24.04:LTS canonical linux-hwe-6.11 All versions
Ubuntu:24.04:LTS canonical linux-hwe-6.14 All versions
Ubuntu:24.04:LTS canonical linux-hwe-6.17 All versions
Ubuntu:24.04:LTS canonical linux-hwe-7.0 < 7.0.0-31.31~24.04.1
Fix: upgrade to 7.0.0-31.31~24.04.1
Ubuntu:24.04:LTS canonical linux-ibm < 6.8.0-1067.68
Fix: upgrade to 6.8.0-1067.68
Ubuntu:24.04:LTS canonical linux-lowlatency < 6.8.0-147.147.1
Fix: upgrade to 6.8.0-147.147.1
Ubuntu:24.04:LTS canonical linux-lowlatency-hwe-6.11 All versions
Ubuntu:24.04:LTS canonical linux-nvidia All versions
Ubuntu:24.04:LTS canonical linux-nvidia-6.11 All versions
Ubuntu:24.04:LTS canonical linux-nvidia-6.17 All versions
Ubuntu:24.04:LTS canonical linux-nvidia-7.0 < 7.0.0-1018.18~24.04.1
Fix: upgrade to 7.0.0-1018.18~24.04.1
Ubuntu:24.04:LTS canonical linux-nvidia-lowlatency All versions
Ubuntu:24.04:LTS canonical linux-nvidia-tegra < 6.8.0-1035.38
Fix: upgrade to 6.8.0-1035.38
Ubuntu:24.04:LTS canonical linux-oem-6.11 All versions
Ubuntu:24.04:LTS canonical linux-oem-6.14 All versions
Ubuntu:24.04:LTS canonical linux-oem-6.17 All versions
Ubuntu:24.04:LTS canonical linux-oem-6.8 All versions
Ubuntu:24.04:LTS canonical linux-oracle < 6.8.0-1064.67
Fix: upgrade to 6.8.0-1064.67
Ubuntu:24.04:LTS canonical linux-oracle-6.14 All versions
Ubuntu:24.04:LTS canonical linux-oracle-6.17 All versions
Ubuntu:24.04:LTS canonical linux-oracle-7.0 < 7.0.0-1011.11~24.04.1
Fix: upgrade to 7.0.0-1011.11~24.04.1
Ubuntu:24.04:LTS canonical linux-raspi All versions
Ubuntu:24.04:LTS canonical linux-raspi-realtime All versions
Ubuntu:24.04:LTS canonical linux-riscv-6.14 All versions
Ubuntu:24.04:LTS canonical linux-riscv-6.17 All versions
Ubuntu:24.04:LTS canonical linux-riscv-7.0 < 7.0.0-31.31.1~24.04.1
Fix: upgrade to 7.0.0-31.31.1~24.04.1
Ubuntu:24.04:LTS canonical linux-xilinx All versions
Ubuntu:Nvidia-BlueField:24.04:LTS canonical linux-bluefield < 6.8.0-1033.38
Fix: upgrade to 6.8.0-1033.38
Ubuntu:Pro:FIPS-updates:24.04:LTS canonical linux-aws-fips < 6.8.0-1067.70+fips1
Fix: upgrade to 6.8.0-1067.70+fips1
Ubuntu:Pro:FIPS-updates:24.04:LTS canonical linux-azure-fips < 6.8.0-1071.79+fips1
Fix: upgrade to 6.8.0-1071.79+fips1
Ubuntu:Pro:FIPS-updates:24.04:LTS canonical linux-fips < 6.8.0-147.147+fips1
Fix: upgrade to 6.8.0-147.147+fips1
Ubuntu:Pro:FIPS-updates:24.04:LTS canonical linux-gcp-fips < 6.8.0-1071.79+fips1
Fix: upgrade to 6.8.0-1071.79+fips1
Ubuntu:Pro:Realtime:24.04:LTS canonical linux-realtime-6.14 All versions
Ubuntu:Pro:Realtime:24.04:LTS canonical linux-realtime-6.17 All versions
Ubuntu:26.04:LTS canonical linux-nvidia-bos < 7.0.0-2018.18
Fix: upgrade to 7.0.0-2018.18
Ubuntu:26.04:LTS canonical linux-oem-7.0 < 7.0.0-1013.13
Fix: upgrade to 7.0.0-1013.13
Ubuntu:26.04:LTS canonical linux < 7.0.0-31.31
Fix: upgrade to 7.0.0-31.31
Ubuntu:26.04:LTS canonical linux-aws < 7.0.0-1012.12
Fix: upgrade to 7.0.0-1012.12
Ubuntu:26.04:LTS canonical linux-azure < 7.0.0-1014.14
Fix: upgrade to 7.0.0-1014.14
Ubuntu:26.04:LTS canonical linux-gcp < 7.0.0-1011.11
Fix: upgrade to 7.0.0-1011.11
Ubuntu:26.04:LTS canonical linux-gke < 7.0.0-1006.7
Fix: upgrade to 7.0.0-1006.7
Ubuntu:26.04:LTS canonical linux-ibm < 7.0.0-1013.13
Fix: upgrade to 7.0.0-1013.13
Ubuntu:26.04:LTS canonical linux-nvidia < 7.0.0-1018.18
Fix: upgrade to 7.0.0-1018.18
Ubuntu:26.04:LTS canonical linux-oracle < 7.0.0-1011.11
Fix: upgrade to 7.0.0-1011.11
Ubuntu:26.04:LTS canonical linux-raspi < 7.0.0-1019.19
Fix: upgrade to 7.0.0-1019.19
Ubuntu:26.04:LTS canonical linux-realtime < 7.0.0-31.31.1
Fix: upgrade to 7.0.0-31.31.1
Ubuntu:26.04:LTS canonical linux-riscv < 7.0.0-31.31.1
Fix: upgrade to 7.0.0-31.31.1
Ubuntu:24.04:LTS canonical linux-azure < 6.8.0-1071.79
Fix: upgrade to 6.8.0-1071.79
Ubuntu:24.04:LTS canonical linux-azure-fde < 6.8.0-1069.76
Fix: upgrade to 6.8.0-1069.76
Ubuntu:24.04:LTS canonical linux-gcp < 6.8.0-1071.79
Fix: upgrade to 6.8.0-1071.79
Ubuntu:24.04:LTS canonical linux-gke < 6.8.0-1066.74
Fix: upgrade to 6.8.0-1066.74
Ubuntu:24.04:LTS canonical linux-gkeop < 6.8.0-1052.56
Fix: upgrade to 6.8.0-1052.56
Ubuntu:Pro:Realtime:24.04:LTS canonical linux-realtime < 6.8.1-1062.63
Fix: upgrade to 6.8.1-1062.63
Ubuntu:26.04:LTS canonical linux-azure-fde < 7.0.0-1013.13
Fix: upgrade to 7.0.0-1013.13
Original advisory text
9p: avoid putting oldfid in p9_client_walk() error path
In the Linux kernel, the following vulnerability has been resolved:

9p: avoid putting oldfid in p9_client_walk() error path

When p9_client_walk() is called with clone set to false, fid aliases
oldfid. If the walk subsequently fails after the request has been sent,
the error path jumps to clunk_fid, which currently calls p9_fid_put(fid)
unconditionally.

This drops a reference to oldfid even though ownership of oldfid remains
with the caller. If this is the last reference, oldfid can be clunked and
destroyed while the caller still expects it to be valid. A later use or
put of oldfid can then trigger a use-after-free or refcount underflow.

Fix this by only putting fid in the clunk_fid error path when it does not
alias oldfid, matching the existing guard in the error path below.

This can be triggered when a multi-component walk is split into multiple
p9_client_walk() calls and a later non-cloning walk fails. A reproducer
and refcount warning logs are available on request.
References
Fix within
Internet-facing 3 days
Internal 60 days
  • Not known to be exploited
  • Can be exploited automatically (estimated)
  • Gives an attacker full control (estimated)
Severity
10.0 Critical
Exploitation
<1% chance of attack within 30 days
Type
CWE-416Use After Free
Timeline
Published19 Jul 2026
Updated4 Nov 2026
First seen19 Jul 2026
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