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CVE-2026-63795— 9p: avoid putting oldfid in p9_client_walk() error path

CVSS 10.0 · Critical EPSS 0.17% · P7

Possible ATT&CK Techniques 1AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 14

VendorProductVersion RangeStatus
LinuxLinuxb48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< b84f46179c806450b89821221ea5bd9a1698aba8affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< a61bdcba4f64c2f90d01461913f429ab151f1ca6affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 6dbe9443d9f5f7fb6d319a7b77108853ae6c6beaaffected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< a7656d368265d085ac9bb85ab31b0cdb72ad8c38affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 1a3860d46e3eb47dbd60339783cdad7904486b9faffected
6.0affected
< 6.0unaffected
… +6 more rows
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I. Basic Information for CVE-2026-63795

Vulnerability Information
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Vulnerability Title
9p: avoid putting oldfid in p9_client_walk() error path
Source: NVD (National Vulnerability Database)
Vulnerability Description
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.
Source: NVD (National Vulnerability Database)
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source: NVD (National Vulnerability Database)
Vulnerability Type
N/A
Source: NVD (National Vulnerability Database)
Vulnerability Title
Linux kernel 安全漏洞
Source: CNNVD (China National Vulnerability Database)
Vulnerability Description
Linux kernel是美国Linux基金会开源的一款操作系统内核。 Linux kernel存在安全漏洞，该漏洞源于p9_client_walk()错误路径中对oldfid的处理不当，可能导致释放后重用或引用计数下溢。以下版本受到影响：6.0版本及之前版本。
Source: CNNVD (China National Vulnerability Database)
CVSS Information
N/A
Source: CNNVD (China National Vulnerability Database)
Vulnerability Type
N/A
Source: CNNVD (China National Vulnerability Database)

Affected Products

VendorProductAffected VersionsCPESubscribe
LinuxLinux b48dbb998d70b7f48c2ec0a15c3cf47136808e4e ~ 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 -
LinuxLinux 6.0 -

II. Public POCs for CVE-2026-63795

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III. Intelligence Information for CVE-2026-63795

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Patches & Fixes for CVE-2026-63795 (6)

Same Patch Batch · Linux · 2026-07-19 · 431 CVEs total

CVE-2026-641429.8 CRITICALksmbd: close durable scavenger races against m_fp_list lookups
CVE-2026-640559.8 CRITICALnet: ethernet: cortina: Carry over frag counter
CVE-2026-640569.8 CRITICALnet: ethernet: cortina: Make RX SKB per-port
CVE-2026-640619.8 CRITICALnetfs: Fix early put of sink folio in netfs_read_gaps()
CVE-2026-639849.8 CRITICALipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()
CVE-2026-640669.8 CRITICALnetfs: Fix netfs_read_to_pagecache() to pause on subreq failure
CVE-2026-640679.8 CRITICALnetfs: Fix missing barriers when accessing stream->subrequests locklessly
CVE-2026-641509.8 CRITICALnetfilter: nft_inner: release local_lock before re-enabling softirqs
CVE-2026-639229.8 CRITICALipv6: exthdrs: refresh nh after handling HAO option
CVE-2026-640689.8 CRITICALnetfs: Fix missing locking around retry adding new subreqs
CVE-2026-639249.8 CRITICALipv6: exthdrs: refresh nh pointer after ipv6_hop_jumbo()
CVE-2026-640699.8 CRITICALnetfs: Fix cancellation of a DIO and single read subrequests
CVE-2026-639799.8 CRITICALnet/handshake: hand off the pinned file reference to accept_doit
CVE-2026-639789.8 CRITICALnet/handshake: Drain pending requests at net namespace exit
CVE-2026-638009.8 CRITICALpNFS: Fix use-after-free in pnfs_update_layout()
CVE-2026-641259.8 CRITICALnet: bcmgenet: keep RBUF EEE/PM disabled
CVE-2026-638579.8 CRITICALnet: airoha: Do not read uninitialized fragment address in airoha_dev_xmit()
CVE-2026-641229.8 CRITICALnet/mlx5e: Fix use-after-free in mlx5e_tx_reporter_timeout_recover
CVE-2026-640919.8 CRITICALbatman-adv: tt: fix TOCTOU race for reported vlans
CVE-2026-641029.8 CRITICALRDMA/siw: Reject MPA FPDU length underflow before signed receive math

Showing top 20 of 431 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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