CVE-2026-31437 — netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry
In the Linux kernel, the following vulnerability has been resolved: netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry When a write subrequest is marked NETFS_SREQ_NEED_RETRY, the retry path in netfs_unbuffered_write() unconditionally calls stream->prepare_write() without checking if it is NULL. Filesystems such as 9P do not set the prepare_write operation, so stream->prepare_write remains NULL. When get_user_pages() fails with -EFAULT and the subrequest is flagged for retry, this results in a NULL pointer dereference at fs/netfs/direct_write.c:189. Fix this by mirroring the pattern already used in write_retry.c: if stream->prepare_write is NULL, skip renegotiation and directly reissue the subrequest via netfs_reissue_write(), which handles iterator reset, IN_PROGRESS flag, stats update and reissue internally.
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 0.2% (30-day exploitation probability)+1
- 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)
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 matching the vulnerability class (memory corruption), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Linux | Linux | ≥ 72d08d2839649d1c5efbe375751f4473fa4486af and < a4d1b4ba9754bac3efebd06f583a44a7af52c0ab≥ 0c29f6d63122a0168d67cb8ecde5b4cf7fe4acb0 and < 7a5482f5ce891decbf36f2e6fab1e9fc4a76a684≥ a0b4c7a49137ed21279f354eb59f49ddae8dffc2 and < e9075e420a1eb3b52c60f3b95893a55e77419ce8≥ 6.18.17 and < 6.18.21≥ 6.19.7 and < 6.19.11 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Linux | Linux Kernel | ≥ 6.18.17 and < 6.18.21≥ 6.19.7 and < 6.19.11 | 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 |
|---|---|---|---|---|---|
| 5.5 | CVSS 3.1 | Medium | 1.8 | 3.6 | nvd@nist.gov via NIST National Vulnerability Database |
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) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.16%
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.
- Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
Timeline
What happened to this CVE, newest first.
- 2026
- Affected products added · linux/linux
- Record published
- Fix documented
- CVSS changed · 5.5
- Source status changed · → Analyzed
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
3 on the record
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-99999 ipv4: validate checksum_start before completing checksum 9h
- Unknown CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 9h
- Unknown CVE-2026-98425 wifi: mac80211: don't warn when an IBSS has no channel to scan 1d
- Unknown CVE-2026-98431 RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency 1d
- Unknown CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
- Unknown CVE-2026-98429 RDMA/efa: Keep EQ resources alive while IRQ is registered 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 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-2026-31437 is "netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry", 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 0.16% 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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