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

Quick assessment

Affected
Linux Linux
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

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。

CVSS 10.0 · Critical EPSS 0.50% · P42

Possible ATT&CK Techniques 1 AI

T1203 · Exploitation for Client Execution

Affected Version Matrix 14

VendorProduct Version RangeStatus
Linux Linux b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< b84f46179c806450b89821221ea5bd9a1698aba8 affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< a61bdcba4f64c2f90d01461913f429ab151f1ca6 affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 6dbe9443d9f5f7fb6d319a7b77108853ae6c6bea affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< a7656d368265d085ac9bb85ab31b0cdb72ad8c38 affected
b48dbb998d70b7f48c2ec0a15c3cf47136808e4e< 1a3860d46e3eb47dbd60339783cdad7904486b9f affected
6.0 affected
< 6.0 unaffected
… +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: CVE Program / CVE List V5
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: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5
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

Vendor Product Affected Versions CPE Subscribe
Linux Linux b48dbb998d70b7f48c2ec0a15c3cf47136808e4e ~ 99c379ca1e221c3d75c7c804ebbf4e5ee37a3070 -
Linux Linux 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 · 429 CVEs total

CVE-2026-64056 9.8 CRITICAL net: ethernet: cortina: Make RX SKB per-port
CVE-2026-64142 9.8 CRITICAL ksmbd: close durable scavenger races against m_fp_list lookups
CVE-2026-64125 9.8 CRITICAL net: bcmgenet: keep RBUF EEE/PM disabled
CVE-2026-63924 9.8 CRITICAL ipv6: exthdrs: refresh nh pointer after ipv6_hop_jumbo()
CVE-2026-63857 9.8 CRITICAL net: airoha: Do not read uninitialized fragment address in airoha_dev_xmit()
CVE-2026-53399 9.8 CRITICAL nfsd: release layout stid on setlease failure
CVE-2026-53398 9.8 CRITICAL NFSD: Fix SECINFO_NO_NAME decode error cleanup
CVE-2026-63984 9.8 CRITICAL ipv6: rpl: fix hdrlen overflow in ipv6_rpl_srh_decompress()
CVE-2026-64047 9.8 CRITICAL net: tls: fix off-by-one in sg_chain entry count for wrapped sk_msg ring
CVE-2026-64025 9.8 CRITICAL bpf, skmsg: fix verdict sk_data_ready racing with ktls rx
CVE-2026-63886 9.8 CRITICAL scsi: target: iscsi: Validate CHAP_R length before base64 decode
CVE-2026-63979 9.8 CRITICAL net/handshake: hand off the pinned file reference to accept_doit
CVE-2026-64033 9.8 CRITICAL RDMA/rtrs: Fix use-after-free in path file creation cleanup
CVE-2026-64150 9.8 CRITICAL netfilter: nft_inner: release local_lock before re-enabling softirqs
CVE-2026-63887 9.8 CRITICAL scsi: target: iscsi: Bound iscsi_encode_text_output() appends to rsp_buf
CVE-2026-64162 9.8 CRITICAL idpf: fix read_dev_clk_lock spinlock init in idpf_ptp_init()
CVE-2026-63808 9.8 CRITICAL exfat: fix potential use-after-free in exfat_find_dir_entry()
CVE-2026-64055 9.8 CRITICAL net: ethernet: cortina: Carry over frag counter
CVE-2026-64035 9.8 CRITICAL igc: set tx buffer type for SMD frames
CVE-2026-63888 9.8 CRITICAL scsi: target: iscsi: Fix CRC overread and double-free in iscsit_handle_text_cmd()

Showing top 20 of 429 CVEs. View all on vendor page &rarr; →

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

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