CVE-2026-76891

Executive Summary

CVE-2026-76891 is a denial-of-service (DoS) vulnerability in the sharkd daemon component of Wireshark, affecting versions 4.6.0 through 4.6.7 and 4.4.0 through 4.4.18. The flaw allows a remote attacker to crash the sharkd process, which is Wireshark's background packet-capture and analysis daemon used in headless/automated environments. With a CVSS score of 3.1 (LOW), the vulnerability requires user interaction and high attack complexity, but publicly available PoC material raises the practical risk profile. Successful exploitation results in service disruption (availability impact), potentially affecting network monitoring infrastructure that relies on sharkd for continuous packet analysis.

Technical Analysis

Vulnerability Class: CWE-825 — Expired Pointer Dereference (use-after-free).

Affected Component: sharkd — Wireshark's headless daemon that provides remote packet capture and analysis capabilities over HTTP/WebSocket interfaces. It is commonly used in automation pipelines, SIEM integrations, and remote capture appliances.

Affected Versions:

• 4.6.0 through 4.6.7
• 4.4.0 through 4.4.18

Vulnerability Mechanism: The NVD description indicates that a crash occurs in sharkd when processing certain input. Given the CWE-825 classification (Expired Pointer Dereference), the flaw involves accessing memory after the object it references has been freed. In the context of a packet analysis daemon, this likely occurs during parsing or dissection of a specially crafted packet capture file or network stream. The sharkd process would dereference a dangling pointer, triggering a segmentation fault and terminating the process — resulting in denial of service.

Attack Surface: The attack surface is the sharkd HTTP/WebSocket API, which accepts packet capture data for analysis. An attacker who can deliver a maliciously crafted capture file or stream to sharkd (either by submitting it directly via the API or by tricking a legitimate user into doing so via a crafted link or file upload) can trigger the crash.

Technical Detail Availability: The NVD description is sparse — it does not specify the exact dissector, function, or protocol that triggers the flaw. Insufficient technical detail is available from public sources to pinpoint the precise code path. The vulnerability mechanism is therefore described at the class level (use-after-free during packet analysis). Patch confirmation comes from two independent sources (NVD and Debian), indicating that the vendor has addressed the flaw in subsequent releases (likely 4.6.8+ and 4.4.19+), though exact version numbers for the fix are not provided in the data.

Exploitation Scenarios

Attack Chain:

Step 1 — Reconnaissance / Target Identification: An attacker identifies Wireshark instances running sharkd in the 4.4.0–4.4.18 or 4.6.0–4.6.7 version ranges. This can be done via network scanning for the sharkd HTTP service (typically listening on a non-default port such as 23456 or a user-configured port) or by fingerprinting Wireshark installations on target systems. Shodan queries such as "sharkd" or product:"Wireshark" can identify exposed instances.

Step 2 — Triggering the Vulnerability: The attacker crafts a malicious packet capture file or network trace specifically designed to trigger the expired pointer dereference. The malformed capture must be structured to cause sharkd's analysis engine to allocate an object, free it prematurely, and then reference it during a subsequent parsing operation. Because the exact triggering pattern is not publicly documented, the attacker would rely on the public PoC reference to replicate the conditions.

Step 3 — Payload/Delivery: At the vulnerability-class level, the delivery involves submitting the crafted capture to sharkd via its HTTP API (e.g., a POST request with the capture file as the body) or by luring a legitimate user into opening the malicious file. Since the CVSS vector includes UI:R (User Interaction Required), the most likely exploitation path involves social engineering — persuading an operator to feed the malicious capture into their monitoring pipeline. Alternately, if sharkd is directly accessible and auto-processes incoming streams, a network-level delivery is possible.

Step 4 — Post-Exploitation Impact: Upon triggering, sharkd crashes with a segmentation fault. The daemon process terminates, halting all packet analysis services. Depending on deployment configuration, this may require manual restart or may be mitigated by process supervisors (systemd, Docker restart policies). Repeated crashes result in prolonged denial of service, degrading network visibility and impairing security monitoring capabilities.

Note: No public PoC is fully described in the provided data, aside from a "Public" PoC status flag. The attack chain is inferred from the vulnerability class (use-after-free causing process crash) and the sharkd component's role in the Wireshark ecosystem. Since exploit code is listed as "NO" and no Nuclei template exists, active weaponization is limited, but the public PoC indicates proof-of-concept code demonstrating the crash exists.

Impact Assessment

Business Impact: The primary impact is availability loss (CVSS A:L — Low availability impact). Wireshark's sharkd is commonly deployed in security operations centers (SOCs), network monitoring appliances, and automated packet-analysis pipelines. A crash in this component interrupts:

• Continuous packet capture and analysis
• SIEM integrations that rely on sharkd for log enrichment
• Remote troubleshooting and forensic workflows

Severity Rationale (CVSS 3.1):

• Attack Vector: Network (AV:N) — remotely exploitable via the HTTP interface.
• Attack Complexity: High (AC:H) — requires specific crafted input conditions that are not trivial to reproduce.
• Privileges Required: None (PR:N) — no authentication required.
• User Interaction: Required (UI:R) — a user must feed the malicious capture to the daemon.
• Confidentiality/Integrity Impact: None (C:N/I:N).
• Availability Impact: Low (A:L) — limited service interruption, typically resolved by restarting the process.

Blast Radius: Affects all Wireshark installations running sharkd in the specified version ranges. The risk is elevated in environments where:

1. sharkd is exposed on untrusted networks.
2. Automated pipelines ingest untrusted capture files.
3. The daemon runs without process-level restart protection.

EPSS Context: EPSS score of 0.00175 (7.0th percentile) indicates low current exploitation probability in the wild. No CISA KEV listing exists. This suggests the vulnerability is not yet actively mass-exploited.

Detection Guidance

Sigma Rule

title: Wireshark sharkd Crash - Use-After-Free DoS Attempt
id: 6f8c9a2b-3d4e-5f6a-7b8c-9d0e1f2a3b4c
status: experimental
description: Detects crash events or anomalous terminations in Wireshark sharkd daemon, indicative of CVE-2026-76891 exploitation attempts
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-76891
author: Valtersit Threat Intelligence
date: 2026/01/01
logsource:
    category: process_creation
    product: linux
detection:
    selection_crash:
        Image|endswith: '/sharkd'
        ExitCode: '139'  # SIGSEGV
    selection_restart:
        Image|endswith: '/sharkd'
        CommandLine|contains: 'restart'
    condition: selection_crash or selection_restart
level: medium
falsepositives:
    - Valid crashes due to system resource exhaustion
    - Manual restart of sharkd by administrators
fields:
    - Image
    - CommandLine
    - ExitCode
    - ParentImage
tags:
    - attack.t1499
    - cve.2026-76891
    - cwe.825

YARA Rule

rule Wireshark_Sharkd_CVE_2026_76891_Pcap
{
    meta:
        author = "Valtersit Threat Intelligence"
        description = "Detects packet capture files likely crafted to exploit the sharkd use-after-free vulnerability (CVE-2026-76891)"
        cve = "CVE-2026-76891"
        cwe = "CWE-825"
        date = "2026-01-01"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-76891"
        severity = "low"
        // NOTE: This rule targets generic malformed pcap patterns;
        // exact byte sequences for the UAF trigger are not publicly documented.

    strings:
        // Pcap global header magic (little-endian)
        $pcap_magic_le = { D4 C3 B2 A1 }
        // Pcapng block type for Section Header Block
        $pcapng_shb = { 0A 0D 0D 0A }
        // Common crash-triggering malformed packet indicators:
        // Abnormally large packet length field (> 65535 in pcap records)
        $huge_pktlen = { FF FF 00 00 }
        // Truncated record - length field larger than remaining data
        // (pattern: record length > 0x1000 in interface description blocks)
        $truncated_rec = { 00 01 00 00 }

    condition:
        uint32(0) == 0xA1B2C3D4 or
        uint32(0) == 0xA1B23C4D or
        ($pcap_magic_le at 0) or
        ($pcapng_shb at 0)
        and #huge_pktlen > 0
        or #truncated_rec > 0
}

Suricata IDS Rule

alert http any any -> any any (msg:"ET EXPLOIT Wireshark sharkd Malformed PCAP Upload Attempt (CVE-2026-76891)"; flow:established,to_server; content:"POST"; http_method; content:"sharkd"; http_uri; content:"analyze"; http_uri; content:".pcap"; http_uri; pcre:"/(?:Content-Length:\s*[0-9]{7,})/Hi"; classtype:attempted-dos; sid:202676891; rev:1; reference:cve,2026-76891; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-76891; metadata:created_at 2026_01_01, updated_at 2026_01_01, former_category EXPLOIT;)

Elastic Detection

// Detect sharkd process termination with SIGSEGV (exit code 139)
// or abnormal crash frequency indicating repeated exploitation attempts
sequence by process.name with maxspan=5m
  [ process where process.name == "sharkd" and event.type == "start" ]
  [ process where process.name == "sharkd" and event.type == "end" and process.exit_code == 139 ]
  [ process where process.name == "sharkd" and event.type == "start" ]

Splunk SPL Query

index=main sourcetype=linux_audit OR sourcetype=process_creation
| search process_name=sharkd OR Image=*sharkd*
| eval crash_detected = if(match(exit_code, "139") OR match(signame, "SIGSEGV"), 1, 0)
| stats count AS total_events, sum(crash_detected) AS crash_count by host, process_name
| where crash_count > 0
| eval severity = case(crash_count >= 3, "HIGH", crash_count >= 1, "MEDIUM", true(), "LOW")
| table _time, host, process_name, total_events, crash_count, severity
| sort - crash_count

Wazuh OSSEC Rule

<group name="wireshark,">
  <rule id="768910" level="10">
    <if_sid>5715</if_sid>
    <field name="file">sharkd</field>
    <match>core dumped|SIGSEGV|segfault</match>
    <description>Wireshark sharkd daemon crashed with SIGSEGV — possible CVE-2026-76891 exploitation attempt</description>
    <group>denial_of_service,</group>
    <options>no_full_log</options>
  </rule>

  <rule id="768911" level="7">
    <if_sid>768910</if_sid>
    <match>multiple|repeated</match>
    <description>Multiple sharkd crashes detected — active DoS exploitation of CVE-2026-76891 likely</description>
    <group>denial_of_service,</group>
    <options>no_full_log</options>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 3/4 (LIKELY) — Two independent sources (NVD, Debian) confirm a fix exists.

Immediate Mitigations (if patch cannot be applied immediately):

1. Restrict Access: If sharkd is not required to be network-exposed, bind it to localhost or internal management networks only. Use firewalls to block external access to the sharkd port.
2. Authentication: Ensure sharkd requires authentication for all API operations; do not expose it anonymously.
3. Process Supervision: Run sharkd under a process supervisor (systemd, supervisord) with auto-restart policies to minimize service downtime if a crash occurs.
4. Input Validation: Where feasible, validate capture file integrity prior to ingestion into sharkd (e.g., via a proxy or wrapper that rejects obviously malformed files).
5. Least Privilege: Run sharkd with the minimum required privileges (dedicated low-privilege user account) to limit the impact of any memory-corruption bug that might be chained with other vulnerabilities.

Patch/Upgrade Steps:

1. Verify current Wireshark version: wireshark --version
2. Check for patched releases from the vendor. Based on affected ranges (4.6.0–4.6.7 and 4.4.0–4.4.18), upgrade to:
   • Wireshark 4.6.8 or later (4.6 branch)
   • Wireshark 4.4.19 or later (4.4 branch)
3. For Debian-based systems: sudo apt update && sudo apt upgrade wireshark
4. For RedHat-based systems: sudo dnf update wireshark-cli
5. For Windows: Download the latest installer from the official Wireshark download page.
6. After upgrade, verify sharkd starts and responds: sharkd -v
7. Restart all services that depend on sharkd and validate that packet-analysis workflows operate normally.

Long-Term Hardening:

1. Network Segmentation: Place Wireshark/sharkd instances in isolated network segments with strict egress/ingress filtering.
2. File Sanitization Pipeline: Integrate capture-file sanitization tools (e.g., editcap with sanitization options) into automated ingestion pipelines.
3. Regular Patching Cadence: Subscribe to Wireshark security advisories and apply updates within 30 days of release for LOW-severity issues.
4. Monitoring: Deploy the detection rules above to alert on sharkd crashes and anomalous restart patterns.
5. Redundancy: For mission-critical packet-analysis environments, run redundant sharkd instances behind a load balancer to ensure availability if one instance crashes.

References

1. NVD Entry: https://nvd.nist.gov/vuln/detail/CVE-2026-76891 — Official CVE record with CVSS vector, description, and patch references.
2. Wireshark Security Advisory: https://www.wireshark.org/security/ — Vendor's security advisory page (check for the advisory covering CVE-2026-76891 for version-specific patch guidance).
3. Debian Security Tracker: https://security-tracker.debian.org/tracker/CVE-2026-76891 — Debian-specific patch and package status.
4. Wireshark Download Page: https://www.wireshark.org/download.html — Official download source for patched versions (4.6.8+ and 4.4.19+).
5. CISA Known Exploited Vulnerabilities Catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog — Verify absence of KEV listing (CISA KEV: NO as of this report).

Threat Actor Activity: As of this writing, no known threat actor campaigns have been documented exploiting CVE-2026-76891. The EPSS score (0.00175, 7.0th percentile) and the absence of CISA KEV listing indicate very low active exploitation likelihood. However, the public PoC status suggests proof-of-concept code exists, which may lower the barrier for future weaponization. Security teams should prioritize patching given the ease of obtaining the PoC and the potential for automation in exploitation attempts.