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CVE-2026-89696— nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref

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.

在 Linux 内核中，以下漏洞已得到修复： nfsd：在 FOREIGN PUTFH 之后阻止非 SAVEFH 操作，以防止空指针解引用 当启用 时， 在 返回 且 为 true 的情况下，可能会以 和 均为 NULL 的状态返回成功。此时会设置 标志位，但复合操作分派循环仅使用该标志位来绕过 检查，却未能阻止后续操作在 为 NULL 的情况下继续执行。 远程客户端可以通过构造一个 COMPOUND 请求来利用此漏洞：该请求中包含一个 inter-SSC COPY 操作（这会导致 将保存的 PUTFH 的 设为

AI Predicted 5.3 Difficulty: Hard

Affected Version Matrix 10

VendorProduct Version RangeStatus
Linux Linux b9e8638e3d9ed8334f1f7071e081860aac37e83e< 35f248bd40b47b229d4999581df45b97daadd977 affected
b9e8638e3d9ed8334f1f7071e081860aac37e83e< 311f7d926630940650447cbd1c932b076b40a6c4 affected
b9e8638e3d9ed8334f1f7071e081860aac37e83e< bf4d338dc8625d70c7f2cb0657d66851a7ac9154 affected
b9e8638e3d9ed8334f1f7071e081860aac37e83e< c59738a00aa51b16adc1b5ceb7c80877168efb4d affected
5.6 affected
< 5.6 unaffected
6.12.109≤ 6.12.* unaffected
6.18.50≤ 6.18.* unaffected
… +2 more rows
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I. Basic Information for CVE-2026-89696

Vulnerability Information
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Vulnerability Title
nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref
Source: CVE Program / CVE List V5
Vulnerability Description
In the Linux kernel, the following vulnerability has been resolved: nfsd: block non-SAVEFH ops after FOREIGN PUTFH to prevent NULL deref When CONFIG_NFSD_V4_2_INTER_SSC is enabled, nfsd4_putfh() can return success with fh_dentry and fh_export both NULL if fh_verify() returns nfserr_stale and putfh->no_verify is true. The NFSD4_FH_FOREIGN flag is set, but the compound dispatch loop only uses this flag to bypass the nfserr_nofilehandle check -- it does not prevent subsequent ops from running with a NULL fh_dentry. A remote client can exploit this by crafting a COMPOUND that includes an inter-SSC COPY (which causes check_if_stalefh_allowed() to set no_verify=true on the saved PUTFH) with an additional op inserted between the source PUTFH and SAVEFH. For example, SETATTR calls fh_want_write() which dereferences fh_export->ex_path.mnt without calling fh_verify() first, causing a NULL pointer dereference in the nfsd kthread. Fix this by gating the dispatch loop: when NFSD4_FH_FOREIGN is set and fh_dentry is NULL, only OP_SAVEFH (needed for the inter-SSC flow) and ops with ALLOWED_WITHOUT_FH (which don't need a resolved filehandle) may proceed. All other ops receive nfserr_stale, per RFC 7862 Section 15.2.3 which specifies that foreign filehandle validation is deferred to the consuming operation and NFS4ERR_STALE returned at that point.
Source: CVE Program / CVE List V5
CVSS Information
N/A
Source: CVE Program / CVE List V5
Vulnerability Type
N/A
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
Linux Linux b9e8638e3d9ed8334f1f7071e081860aac37e83e ~ 35f248bd40b47b229d4999581df45b97daadd977 -
Linux Linux 5.6 -

II. Public POCs for CVE-2026-89696

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III. Intelligence Information for CVE-2026-89696

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Patches & Fixes for CVE-2026-89696 (4)

Same Patch Batch · Linux · 2026-09-11 · 431 CVEs total

CVE-2026-89491 ocfs2: cluster: don't sleep while holding o2hb_live_lock in o2hb_region_pin()
CVE-2026-89477 sctp: fix NULL deref on untransmitted RECONF completion
CVE-2026-89478 sctp: drop a chunk if its transport was removed
CVE-2026-89479 sctp: stop processing a packet once its association is deleted
CVE-2026-89480 nvme-tcp: reject a read that transferred too few bytes
CVE-2026-89482 nvme-tcp: do not accept C2HData based on blk_rq_payload_bytes() alone
CVE-2026-89481 nvme-tcp: fix host memory disclosure on R2T for a read command
CVE-2026-89483 nvme: zero the discard fallback page
CVE-2026-89484 lockd: fix NULL dereference on lockowner allocation failure
CVE-2026-89485 lockd: pin next file across nlm_inspect_file lock-drop
CVE-2026-89486 ipmi: Fix use-after-free of cmd_rcvr in _ipmi_destroy_user()
CVE-2026-89487 openvswitch: only skb_tx_error() a packet we are about to drop
CVE-2026-89488 openvswitch: Fix CT limit teardown use-after-free
CVE-2026-89489 openrisc: fix arbitrary kernel memory access via or1k_atomic syscall
CVE-2026-89500 ring-buffer: Make cpu_buffer::free_page a buffer_data_read_page
CVE-2026-89497 orangefs: skip leading spaces before parsing client debug masks
CVE-2026-89498 orangefs: fix double-free of trailer_buf on readdir copy failure
CVE-2026-89499 ring-buffer: Stop remote reader update when page swap fails
CVE-2026-89496 ocfs2: always run deallocs on copy-on-write completion
CVE-2026-89501 ring-buffer: Hold cpu_buffer::lock when resizing a subbuf

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

IV. Related Vulnerabilities

Same product: Linux
Same vendor: Linux

V. Comments for CVE-2026-89696

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