CVE-2025-21795 — NFSD: fix hang in nfsd4_shutdown_callback
In the Linux kernel, the following vulnerability has been resolved: NFSD: fix hang in nfsd4_shutdown_callback If nfs4_client is in courtesy state then there is no point to send the callback. This causes nfsd4_shutdown_callback to hang since cl_cb_inflight is not 0. This hang lasts about 15 minutes until TCP notifies NFSD that the connection was dropped. This patch modifies nfsd4_run_cb_work to skip the RPC call if nfs4_client is in courtesy state.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.6% (30-day exploitation probability)+7
- Technical severity (medium)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
- Documented patch — git.kernel.org (NIST National Vulnerability Database)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes, errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux |
≥ 26540b8940a2e21582afa61a6fb8af87310bac72 and < efa8a261c575f816c7e79a87aeb3ef8a0bd6b221version 5.19≥ 5.15.154 and < 5.15.179≥ 5.10.220 and < 5.10.235≥ 66af25799940b26efd41ea6e648f75c41a48a2c2 and < 036ac2778f7b28885814c6fbc07e156ad1624d03≥ 66af25799940b26efd41ea6e648f75c41a48a2c2 and < e88d2451cd42e025465d6b51fd716a47b0b3800d≥ 66af25799940b26efd41ea6e648f75c41a48a2c2 and < cedfbb92cf97a6bff3d25633001d9c44442ee854≥ 66af25799940b26efd41ea6e648f75c41a48a2c2 and < 23ad7797c74cd8f7f90617f1e59a8703e2b43908 and 2 more≥ 66af25799940b26efd41ea6e648f75c41a48a2c2 and < 38d345f612503b850c2973e5a879f88e441b34d7≥ 67ef9e5fd737eab2495f2586df7e9ea30caa1b77 and < abed68027ea3ab893ac85cc46a00e2e64a324239 |
Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel | ≥ 5.10.220 and < 5.10.235version 6.14-rc2version 6.14-rc1≥ 6.13 and < 6.13.4≥ 6.7 and < 6.12.16≥ 6.2 and < 6.6.79≥ 5.19 and < 6.1.129≥ 5.15.154 and < 5.15.179 | Vulnerable | NIST National Vulnerability Database |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 7.5 | CVSS 3.1 | High | 3.9 | 3.6 | 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database |
| 7.5 | CVSS 3.1 | High | — | — | Linux via CVE Program (cve.org) e CISA ADP |
| 5.5 | CVSS 3.1 | Medium | 1.8 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
| 5.5 | CVSS 3.1 | Medium | — | — | GitHub, Inc. via GitHub Security Advisories |
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H (score shown at the top: nvd@nist.gov) Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Local/physical vector: focus on endpoint telemetry (EDR) from affected hosts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- Affected products added · linux/linux kernel
- CVSS changed · 5.5
- Source status changed · → Modified
- Record created in this database
- 2025
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 2× References added · Oct 14, 2026 – Oct 14, 2026
- 1× Official description updated · Oct 14, 2026 – Oct 14, 2026
References
16 on the record
- git.kernel.org/stable/c/23ad7797c74cd8f7f90617f1e59a8703e2b43908
- git.kernel.org/stable/c/e88d2451cd42e025465d6b51fd716a47b0b3800d
- git.kernel.org/stable/c/036ac2778f7b28885814c6fbc07e156ad1624d03
- git.kernel.org/stable/c/abed68027ea3ab893ac85cc46a00e2e64a324239
- git.kernel.org/stable/c/efa8a261c575f816c7e79a87aeb3ef8a0bd6b221
- git.kernel.org/stable/c/cedfbb92cf97a6bff3d25633001d9c44442ee854
- git.kernel.org/stable/c/38d345f612503b850c2973e5a879f88e441b34d7
- nvd.nist.gov/vuln/detail/CVE-2025-21795
- cert-portal.siemens.com/productcert/html/ssa-082556.html
- lists.debian.org/debian-lts-announce/2025/05/msg00030.html
- cert-portal.siemens.com/productcert/html/ssa-457936.html
- cert-portal.siemens.com/productcert/html/ssa-019113.html
- cert-portal.siemens.com/productcert/html/ssa-784472.html
- github.com/advisories/GHSA-v47h-hxgq-326f
- lists.debian.org/debian-lts-announce/2025/03/msg00028.html
- cert-portal.siemens.com/productcert/html/ssa-265688.html
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 7h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 7h
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98424 wifi: cfg80211: undo netns switch if renaming the wiphy fails 1d
- Unknown CVE-2026-98426 wifi: mwifiex: fix IRQ leak using wrong index in MSI-X error path 1d
- Unknown CVE-2026-98427 net/sched: codel: bound the dropping loop per dequeue call 1d
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No CISA SSVC assessment.
- No CWE classification.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2025-21795 is "NFSD: fix hang in nfsd4_shutdown_callback", rated Medium. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 5.5 describes technical severity. EPSS 0.64% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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