CVE Intelligence
Critical Memory corruption

CVE-2026-52999 — Linux kernel netfilter nfnetlink_osf out-of-bounds read in TCP option matching

In the Linux kernel, the following vulnerability has been resolved: netfilter: nfnetlink_osf: fix out-of-bounds read on option matching In nf_osf_match(), the nf_osf_hdr_ctx structure is initialized once and passed by reference to nf_osf_match_one() for each fingerprint checked. During TCP option parsing, nf_osf_match_one() advances the shared ctx->optp pointer. If a fingerprint perfectly matches, the function returns early without restoring ctx->optp to its initial state. If the user has configured NF_OSF_LOGLEVEL_ALL, the loop continues to the next fingerprint. However, because ctx->optp was not restored, the next call to nf_osf_match_one() starts parsing from the end of the options buffer. This causes subsequent matches to read garbage data and fail immediately, making it impossible to log more than one match or logging incorrect matches. Instead of using a shared ctx->optp pointer, pass the context as a constant pointer and use a local pointer (optp) for TCP option traversal. This makes nf_osf_match_one() strictly stateless from the caller's perspective, ensuring every fingerprint check starts at the correct option offset.

Published Jun 24, 2026 · Updated Oct 15, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP, GitHub Security Advisories · CNA: Linux

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.
How the score was calculated
  • EPSS 0.6% (30-day exploitation probability)+7
  • Technical severity (critical)+10

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.

Exploitation
Not confirmed
Not in CISA KEV — an absence of record, not proof it is unexploited.
EPSS FIRST
0.59%
ahead of 47% of scored CVEs · Oct 15, 2026
Affects
Linux
Linux and 1 more
CVSS base
9.1
Critical · 3 source(s)

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)
  • 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.

  1. Identify exposed assets running the affected vendor/product/version combinations (Linux Linux, Linux Linux Kernel).
  2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
  3. Apply the fixed version or the patch documented under Remediation.
  4. 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.

VendorProductVersionsStatusSource
Linux Linux version 5.0≥ 4.20.13 and < 4.21≥ 4.19.26 and < 4.20version 8316b60582facd4068fb0916c4db2418c21b7174version 0c1054e0e5fdef2369fb089e94def978bd209e1f≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < f5ca450087c3baf3651055e7a6de92600f827af3≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < edb78a142d2e5948e63647c0646aa7e7886935f0≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 21883587593d7c8bb519a79460a0b5bc5ffbdabd
and 5 more ≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 70a3f31d25cf2ec9d4ddfa408120171ead955623≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 32e50f92c7cf3f4eba29622179a5fcdc2aebab41≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 1e19a07291bb8682c14c39a64725a3ae54ab8ccc≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 1c136f2c44a5913646bac85303612fd0825197a0≥ 1a6a0951fc009f6d9fe8ebea2d2417d80d54097b and < 0145548346c4a30981a870a8ca00eac46ba27e85
Vulnerable CVE Program (cve.org) e CISA ADP
Linux Linux Kernel version 5.0-rc8≥ 4.19.26 and < 4.20version 5.0-rc7version 5.0-rc6version 5.0-rc5version 5.0≥ 6.19 and < 7.0.10≥ 6.13 and < 6.18.33
and 6 more ≥ 6.7 and < 6.12.91≥ 6.2 and < 6.6.141≥ 5.16 and < 6.1.175≥ 5.11 and < 5.15.209≥ 5.0.1 and < 5.10.258≥ 4.20.13 and < 5.0
Vulnerable NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

ScoreVersionSeverityExpl.ImpactScored by
9.1 CVSS 3.1 Critical 3.9 5.2 416baaa9-dc9f-4396-8d5f-8c081fb06d67 via NIST National Vulnerability Database
9.1 CVSS 3.1 Critical — — GitHub, Inc. via GitHub Security Advisories
9.1 CVSS 3.1 Critical — — Linux via CVE Program (cve.org) e CISA ADP
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H (score shown at the top: 416baaa9-dc9f-4396-8d5f-8c081fb06d67)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-125 · Out-of-bounds Read

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 15, 2026 · 3 reading(s) · max 0.59%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

  • Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
  • Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.
web/proxy/WAF logsnetwork IDS/IPSendpoint telemetry (EDR)crash dumps

Analysis and videos

CVE-2026-52999: Linux kernel netfilter nfnetlink_osf out-of-bounds read in TCP option matching
The Linux kernel netfilter component nfnetlink_osf has an out-of-bounds read (CWE-125) during TCP option matching for OS fingerprints. A shared parsing pointer was not restored between fingerprint checks, so later checks could read invalid data and fail. The CNA-supplied CVSS 3.1 score is 9.1 (critical), and the record lists no KEV entry or confirmed exploitation.

Timeline

What happened to this CVE, newest first.

  • 2026
  • Affected products added · linux/linux
    Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
  • Record published
    Oct 13, 2026
  • Fix documented
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVSS changed · 9.1
    Oct 13, 2026 · NIST National Vulnerability Database
  • Source status changed · → Modified
    Oct 13, 2026 · NIST National Vulnerability Database
  • Record created in this database
    Oct 13, 2026 · NIST National Vulnerability Database
  • CVE published
    Jun 24, 2026 · Linux

Source activity

Repeated readings are counted rather than listed.

  • 2× References added · Oct 14, 2026 – Oct 15, 2026
  • 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

12 on the record

Elsewhere on this site

Linux
every CVE for this vendor
Memory corruption
same class
CWE-125
other pages naming this weakness

Related CVEs (same products)

  • CVE-2026-99999 ipv4: validate checksum_start before completing checksum 16h
  • CVE-2026-98432 ipv4: free inet_opt and ireq_opt after an RCU grace period 16h
  • CVE-2026-98431 RDMA/uverbs: Fix mmap_lock/disassociation_lock circular dependency 1d
  • CVE-2026-98430 RDMA/efa: Keep admin queues alive while IRQ is registered 1d
  • CVE-2026-98429 RDMA/efa: Keep EQ resources alive while IRQ is registered 1d
  • CVE-2026-98428 ALSA: usb: 6fire: Avoid embedded URBs 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-2026-52999 is "Linux kernel netfilter nfnetlink_osf out-of-bounds read in TCP option matching", rated Critical. It affects Linux (Linux); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.1 describes technical severity. EPSS 0.59% 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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