CVE-2026-45751

Executive Summary

CVE-2026-45751 is a use-after-free (CWE-416) vulnerability in Suricata, the widely deployed open-source network Intrusion Detection System (IDS), Intrusion Prevention System (IPS), and Network Security Monitoring (NSM) engine. The flaw resides in Suricata's inspection-buffer helper, which can leave an inspection pointer referencing freed memory after a chained transform (specifically a dotprefix transform chained after another transform) forces the backing buffer to be reallocated. Successful triggering crashes the inspection engine, causing a denial-of-service (availability impact); the flaw is rated CVSS 5.9 (AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H). Exploitation requires a specific—but non-malicious—rule to be loaded and matching network traffic to be processed, meaning affected deployments are those running vulnerable Suricata versions with such rule chains in production.

Technical Analysis

The vulnerability class is a use-after-free (CWE-416). Per the NVD description, Suricata's inspection-buffer helper contains a logic defect whereby, after a chained transform causes the backing buffer to be reallocated, an inspection pointer continues to reference the freed (original) memory region. The dangling pointer is then dereferenced during subsequent inspection, producing undefined behavior that in practice manifests as a crash of the detection engine.

Two elements must coincide for the defect to be reachable:

1. A specific rule configuration. The rule must chain the dotprefix transform after another transform. Suricata's rule-transform mechanism allows a rule keyword to be rewritten/normalized before matching; chaining transforms means the output of one transform feeds into the next. The NVD text explicitly states the issue "requires a specific but not malicious rule," and the documented workaround is to "avoid rules that chain dotprefix transform after another one." This confirms the trigger is a rule authoring pattern, not attacker-controlled rule content.

2. Specific network traffic processing. The bug "is reached during a specific network traffic processing." That is, the offending rule's transform chain must be evaluated against traffic that matches the rule's preconditions, causing the inspection-buffer helper to run the chained transform path and reallocate the backing buffer while a stale pointer is retained.

The root cause is a lifetime/ownership error in the inspection-buffer helper: buffer reallocation invalidates prior pointers, but the inspection pointer is not refreshed to the new allocation before use. Because the freed memory may be reused, dereferencing the stale pointer yields a crash (availability loss). The CVSS vector (AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H) reflects: remotely reachable over the network, high attack complexity (requires the specific rule + specific traffic), no privileges, no user interaction, no scope change, no confidentiality impact, no integrity impact, and high availability impact.

Note on precision: The NVD description does not disclose the affected source file, function names, or the exact transform chain (beyond dotprefix). No public PoC, exploit code, or Nuclei template exists. No specific code paths beyond the described mechanism should be assumed.

Exploitation Scenarios

No public proof-of-concept is available; the attack chain below is inferred from the vulnerability class (use-after-free reachable via a rule-transform + traffic pattern), consistent with the NVD description.

1. Reconnaissance / target identification. An adversary does not directly "find" this flaw remotely; the precondition is an operator-side configuration. An attacker first identifies whether a target network is protected by Suricata (e.g., version fingerprinting through management interfaces, telemetry, or incidental exposure of Suricata artifacts via Shodan-style reconnaissance) and whether the deployment runs a vulnerable version (< 7.0.16 / < 8.0.5). Because the trigger rule is "specific but not malicious," the attacker cannot author it remotely—they must rely on it already being present in the target's ruleset.

2. Triggering the specific flaw class. The use-after-free is triggered when Suricata processes traffic that matches the chained-transform rule. The rule must chain dotprefix after another transform; when the backing buffer is reallocated during that chained transform, the inspection pointer is left referencing freed memory. The attacker's only controllable input is network traffic: by sending traffic whose characteristics satisfy the rule's match conditions, the attacker induces evaluation of the vulnerable transform path.

3. Payload / execution method (vulnerability-class level). This is not a code-execution primitive described by the vendor. The exploitation "payload" is simply network traffic crafted to match the offending rule's preconditions. There is no described mechanism for memory corruption leading to remote code execution; the described outcome is dereference of freed memory causing engine failure. No shellcode, ROP chain, or specific memory-overwrite technique is implied by the data.

4. Post-exploitation impact. The impact is availability loss: the Suricata detection engine crashes. In IDS mode, this can create a monitoring gap—while the sensor is down or restarting, malicious traffic may pass uninspected. In IPS mode, a crash can either drop inline traffic (denial of service for the protected segment) or fail open depending on configuration, either of which degrades network availability and defense-in-depth. There is no described confidentiality or integrity impact.

Because the trigger requires a non-malicious rule already loaded by the defender, this is best characterized as an operator-induced crash condition that can be remotely activated by traffic—not a weaponized remote exploit.

Impact Assessment

• CVSS 3.1 base score: 5.9 (Medium). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H.
• Confidentiality (C:N): No impact described.
• Integrity (I:N): No impact described.
• Availability (A:H): High—the detection engine crashes on dereference of freed memory.
• Attack Vector (AV:N): Network-reachable; triggered by traffic.
• Attack Complexity (AC:H): High—requires both the specific rule configuration and specific traffic.
• Privileges Required (PR:N) / User Interaction (UI:N): None required.
• Affected systems: Any deployment running Suricata versions prior to 7.0.16 or 8.0.5 that loads a rule chaining dotprefix after another transform. This includes enterprise IDS/IPS sensors, NSM deployments, inline prevention gateways, and cloud/edge network security nodes.
• Blast radius: A single crash affects the sensor processing the matching traffic. In inline IPS deployments, a crash can interrupt traffic forwarding for protected segments. Repeated triggering can cause repeated outages, and a monitoring gap during restart can be leveraged to slip malicious traffic past inspection.
• Exploitability: No public exploit, PoC, or Nuclei template. EPSS not yet scored by FIRST.org (no value available). Not listed in CISA KEV.

Detection Guidance

Sigma Rule

title: Suricata Inspection-Buffer Use-After-Free Crash (CVE-2026-45751)
id: 9f2a7c14-4575-4b51-9a6e-2026cve4575
status: experimental
description: Detects Suricata process crashes indicative of the inspection-buffer use-after-free triggered by rules chaining the dotprefix transform.
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-45751
author: valtersit.com
date: 2026/01/01
tags:
  - attack.t1190
logsource:
  product: linux
  service: syslog
detection:
  selection_crash:
    - 'suricata'
  keywords:
    - 'SIGSEGV'
    - 'segfault'
    - 'BACKTRACE'
    - 'use-after-free'
    - 'inspection buffer'
  condition: selection_crash and keywords
fields:
  - host
  - process
  - message
falsepositives:
  - Other Suricata crashes unrelated to this CVE
level: medium

YARA Rule

rule CVE_2026_45751_Suricata_InspectionBuffer_UAF
{
    meta:
        author = "valtersit.com"
        description = "Detects crash artifacts referencing Suricata inspection-buffer use-after-free (CVE-2026-45751)"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-45751"
        date = "2026-01-01"
        cve = "CVE-2026-45751"
    strings:
        $s1 = "inspection-buffer" ascii nocase
        $s2 = "dotprefix" ascii nocase
        $s3 = "use-after-free" ascii nocase
        $s4 = "SIGSEGV" ascii
        $s5 = "suricata" ascii nocase
    condition:
        filesize < 5MB and
        (uint16(0) == 0x457f or uint32(0) == 0x464c457f) and
        (($s1 and $s2) or ($s3 and $s5) or ($s4 and $s5))
}

Suricata IDS Rule

alert tcp any any -> any any (msg:"CVE-2026-45751 Suricata inspection-buffer UAF trigger - dotprefix chained transform rule traffic"; flow:to_server,established; content:"|00|"; depth:1; threshold: type limit, track by_src, count 1, seconds 60; metadata:cve CVE-2026-45751, created_at 2026_01_01; reference:url,nvd.nist.gov/vuln/detail/CVE-2026-45751; classtype:attempted-dos; sid:9045751; rev:1;)

Note: The trigger traffic is not distinguishable by a stable, protocol-specific signature in the provided data. This rule is a generic visibility placeholder keyed to the CVE metadata and the transport layer; defenders should rely primarily on engine process health monitoring and rule-configuration auditing rather than network signatures for this flaw.

Elastic Detection

process where process.name == "suricata" and
  (event.action == "crashed" or event.action == "exit" or event.reason == "signal") and
  process.exit_code in (-11, 139)

Splunk SPL Query

index=syslog OR index=linux host=* sourcetype=syslog "suricata"
| search ("SIGSEGV" OR "segfault" OR "BACKTRACE" OR "use-after-free")
| stats count min(_time) as first_seen max(_time) as last_seen by host, process, message
| sort - last_seen

Wazuh OSSEC Rule

<group name="suricata,cve-2026-45751,">
  <rule id="100751" level="10">
    <decoded_as>syslog</decoded_as>
    <match>suricata</match>
    <regex>SIGSEGV|segfault|BACKTRACE|use-after-free</regex>
    <description>Suricata process crash possibly related to CVE-2026-45751 inspection-buffer use-after-free</description>
    <mitre>
      <id>T1190</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). The NVD description states fixes ship in Suricata 7.0.16 and 8.0.5, but no vendor advisory, commit, tag, or package artifact has been confirmed by tracked patch sources. Treat status as unpatched until the fixed releases are verified from the authoritative upstream project and your distribution's package repositories.

1. Immediate mitigations (apply now):

   • Remove/avoid the offending rule pattern. Apply the documented workaround: do not load rules that chain the dotprefix transform after another transform. Audit your ruleset for any transform chaining involving dotprefix and disable those rules until patched.
   • Segregate rule management. Restrict who can author or push rules with transform chains, and validate rule configs in a staging sensor before production rollout.
   • Process supervision. Configure systemd or your supervisor to auto-restart Suricata on crash, and monitor for SIGSEGV/exit code 139 to detect outages quickly.
   • Fail-open vs fail-closed review. For inline IPS deployments, review behavior on engine crash to avoid unplanned outages; evaluate whether fail-open is acceptable for the protected segment.

2. Patch/upgrade steps:

   • Verify fixed releases (7.0.16, 8.0.5) from the upstream Suricata project and your distribution vendor; confirm CVE-2026-45751 is addressed in the changelog.
   • Upgrade IDS/IPS sensors to the patched version following your change-control process.
   • After upgrading, re-enable any previously disabled rules only after confirming the fix, and re-validate transform-chain rules in staging.
   • Re-baseline rule sets and confirm the dotprefix chaining pattern no longer triggers reallocation-related faults.

3. Long-term hardening:

   • Add ruleset CI/linting that flags risky transform chaining patterns.
   • Maintain a staged rollout pipeline for rule updates with canary sensors.
   • Monitor engine health metrics (crash counts, restart frequency, uptime) as a security control, not just operations.
   • Track upstream security advisories and subscribe to the Suricata project's release feed; this flaw is a reminder that rule configuration is part of the attack surface.

References

• NVD — CVE-2026-45751: https://nvd.nist.gov/vuln/detail/CVE-2026-45751
• Suricata project (upstream) — release/security information: https://suricata.io/
• CWE-416 — Use After Free: https://cwe.mitre.org/data/definitions/416.html
• FIRST EPSS — CVE-2026-45751 (not yet scored at time of writing): https://api.first.org/data/v1/epss?cve=CVE-2026-45751
• CISA Known Exploited Vulnerabilities catalog (CVE-2026-45751 not listed): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

Threat actor / exploit-in-the-wild evidence: None. No public PoC, exploit code, or Nuclei template exists; the CVE is not in CISA KEV; EPSS is unscored. There are no known threat actor campaigns associated with CVE-2026-45751 at the time of writing. The primary risk today is availability disruption to network inspection coverage, triggerable only in environments that already load the specific chained-transform rule pattern.