CVE-2026-76886

Executive Summary

CVE-2026-76886 is a denial-of-service vulnerability in the Wireshark C12.22 protocol dissector, affecting Wireshark versions 4.6.0 through 4.6.7 and 4.4.0 through 4.4.18. A remote attacker can craft malicious network traffic that, when captured and analyzed by Wireshark, triggers a crash in the C12.22 dissector, leading to service interruption for security analysts, network engineers, and any automated packet analysis pipelines relying on this tool. The vulnerability is classified under CWE-122 (Heap-Based Buffer Overflow) and carries a CVSS score of 8.1 with a publicly available proof-of-concept, though the EPSS score (0.00317) suggests limited active exploitation in the wild to date.

Technical Analysis

The C12.22 protocol is an application-layer protocol defined by ANSI C12.22, used primarily in the utility industry for communication between smart metering devices, data concentrators, and utility head-end systems over networks including TCP/IP. Wireshark implements a protocol dissector for C12.22 to enable analysis of smart grid traffic — a niche but operationally relevant area for utilities, energy sector SOCs, and industrial control system (ICS) security teams.

The vulnerability identified as CVE-2026-76886 resides in the C12.22 dissector and is a heap-based buffer overflow (CWE-122). A heap-based buffer overflow occurs when a program writes data beyond the allocated boundary of a heap memory block. In the context of a protocol dissector, this typically happens during the parsing of length-prefixed fields or variable-length data structures where the dissector trusts attacker-controlled length or count values without adequate validation against the actual size of the allocated buffer.

The attack mechanism operates as follows: an attacker crafts a network packet containing malformed C12.22 protocol data. When Wireshark (or a headless tool like tshark) captures or processes this packet, the dissector reads the embedded length field and subsequently performs a memory copy or write operation into a heap-allocated buffer. If the declared length exceeds the allocated buffer size, the write operation overflows the heap boundary, causing memory corruption. The immediate consequence is a segmentation fault or assertion failure that crashes the entire Wireshark application or the packet-processing thread.

The NVD description does not provide the specific function names, field identifiers, or exact code paths within the C12.22 dissector that are vulnerable. Consequently, the precise parsing flaw — whether it involves an APDU length field, a block size parameter, or a nested TLV structure — cannot be stated with certainty from the available data. What is clear is that the flaw is reachable via network input without requiring authentication, and the parsing of attacker-controlled network data triggers the memory corruption.

The attack surface is significant because Wireshark automatically dissects incoming packets in live capture mode, and also processes pre-captured packet capture (PCAP) files in offline mode. A crafted PCAP file containing malicious C12.22 traffic can be weaponized as a one-click attack vector: the attacker delivers the PCAP (via email attachment, web download, or USB), and when the analyst opens the file in Wireshark, the dissector crashes. Similarly, in live capture environments (e.g., a SOC analyst capturing on a SPAN port or network TAP), a single malicious packet on the wire will trigger the crash upon processing.

The lack of authentication requirement, combined with the network-based attack vector, contributes to the high CVSS base score of 8.1. The confidentiality, integrity, and availability impacts are all rated High in the CVSS vector (C:H/I:H/A:H), which theoretically suggests potential for more than just a crash. However, with no public exploit code demonstrating code execution, the realistic near-term impact is limited to denial of service. Heap overflows in dissectors have historically been escalated to remote code execution; however, modern memory protections (ASLR, DEP on Windows, and similar on Linux) substantially raise the bar for reliable exploitation.

Exploitation Scenarios

The attack chain for CVE-2026-76886 is centered on the processing of malicious network traffic by the vulnerable Wireshark C12.22 dissector. The following steps describe the exploitation progression based on the vulnerability class and available intelligence:

Step 1 — Reconnaissance / Target Identification: The attacker identifies organizations or individuals who regularly use Wireshark for network analysis, with a focus on energy sector entities, utility companies, or ICS/SCADA security teams who are most likely to analyze C12.22 traffic. From a remote perspective, an attacker can send a malicious packet onto a network segment where Wireshark is actively capturing (e.g., a network with a permanent packet capture appliance running tshark). Alternatively, targeted delivery of a crafted PCAP file via phishing email is an effective vector since analysts frequently open PCAP attachments from external sources.

Step 2 — Triggering the Flaw: The attacker crafts an ethernet or IP packet containing a C12.22 application-layer message with deliberately malformed length fields or oversized data structures designed to overflow the heap buffer in the dissector. In live capture mode, the packet is transmitted once to the target network. In offline mode, the attacker saves the malicious packet data as a PCAP file and delivers it to the victim. The moment Wireshark parses the C12.22 message, the vulnerable code path is executed.

Step 3 — Payload Execution at Vulnerability-Class Level: As a heap-based buffer overflow, the payload is the oversized field data that causes the write operation to exceed the allocated heap buffer. The overflow corrupts adjacent heap metadata or application data structures, which leads to an invalid memory access. In the absence of successful memory layout manipulation, the corruption manifests as a crash. The high attack complexity (AC:H) in the CVSS vector reflects the difficulty of shaping the heap layout reliably for code execution; most attempts will result in a crash rather than arbitrary command execution.

Step 4 — Post-Exploitation Impact: In the most common scenario, the result is a denial-of-service condition: the Wireshark application terminates, interrupting live capture sessions, stopping automated analysis scripts, and requiring manual restart. For organizations running continuous packet capture or automated traffic analysis pipelines using tshark in a service capacity, repeated exploitation attacks can create an extended outage of network visibility, effectively blinding the security team during a coordinated incident. If a working memory corruption exploit were developed that achieves code execution, the impact would escalate to the full C:H/I:H/A:H profile indicated in the CVSS score, potentially allowing an attacker to take over the analyst workstation and pivot from there.

The public PoC availability increases the urgency of patching, though the EPSS score of 0.00317 (23.9th percentile) indicates that active weaponization in the wild remains limited as of the scoring date.

Proof of Concept Intelligence

PUBLIC PoC CONFIRMED.

1. Exploit Type: The public PoC represents a denial-of-service (DoS) exploit targeting the heap-based buffer overflow in the C12.22 dissector. It likely consists of a crafted PCAP file or packet capture fragment containing the malicious C12.22 message sequence needed to trigger the crash. The PoC demonstrates the ability to reliably crash Wireshark or tshark when the malicious input is parsed.

2. Capabilities Granted: The primary capability is disruption of network analysis operations. An attacker using this PoC can: (a) crash any Wireshark instance that processes the malicious capture, (b) interrupt automated packet analysis pipelines running tshark, and (c) degrade network visibility for security teams during incident response or monitoring activities. If the underlying overflow were further developed into a code-execution primitive, the PoC could serve as a foundation for remote code execution on the analyst's machine — though no such escalation is publicly confirmed.

3. Technical Barriers to Exploitation: The barriers are moderate. The attacker does not need authentication to craft the malicious traffic. For live network exploitation, the attacker must have the ability to inject packets into a network segment where Wireshark is actively capturing; this requires either network adjacency, a foothold on the network, or the ability to send crafted traffic to a monitor port. For PCAP-based exploitation, the attacker must successfully trick the victim into opening the malicious file — a social engineering component. The high attack complexity (AC:H) in the CVSS vector reflects the difficulty of reliably achieving more than a crash due to heap layout challenges and modern memory protection mechanisms.

4. PoC Access: PoC code and exploitation artifacts are available through the ValtersIT API Pro tier. Access is granted exclusively to authorized security testing professionals and researchers for legitimate vulnerability validation, penetration testing, and defensive detection engineering purposes. All access is logged and monitored; improper use or redistribution violates the terms of service.

Impact Assessment

Business Impact: The vulnerability targets a network diagnostics tool that is ubiquitous across security operations centers, network engineering teams, and ICS/SCADA environments. While the direct impact is a temporary denial of service on the analysis tool itself, the downstream consequences for an organization can include: loss of network visibility during an active incident, delayed forensic analysis of captured traffic, interruption of compliance-related packet retention pipelines, and reputational damage if the attack disrupts critical infrastructure monitoring.

Affected Systems: All Wireshark installations running versions 4.6.0 to 4.6.7 or 4.4.0 to 4.4.18 are vulnerable. This includes the graphical Wireshark application, the command-line tshark utility, and any third-party tool that embeds Wireshark's dissector libraries (libwireshark). Debian-based Linux distributions are confirmed affected through the Debian security tracker. The energy and utility sector is disproportionately affected given the C12.22 protocol's dedicated use in smart metering infrastructure.

Blast Radius: The CVSS vector (CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H) indicates a network-exploitable vulnerability with no privileges and no user interaction required. The scope is Unchanged (U), meaning the compromise is contained to the affected component. The High ratings for confidentiality, integrity, and availability represent the theoretical ceiling if heap exploitation achieves code execution; realistically, near-term impact is confined to the availability dimension (crash/DoS). Organizations running automated capture pipelines face a higher operational risk because a single malicious packet on a monitored segment can repeatedly crash capture services without any human interaction.

Detection Guidance

Sigma Rule

title: Wireshark C12.22 Dissector Heap Overflow Attempt
id: 6dc1b45c-3a4f-4e8b-9f2d-7a1c3d5e8f90
status: experimental
description: Detects network traffic attempting to exploit CVE-2026-76886, a heap-based buffer overflow in the Wireshark C12.22 protocol dissector.
author: ValtersIT Threat Intelligence
date: 2026/05/15
tags:
    - attack.t1499
    - cve.2026.76886
    - cwe.122
logsource:
    category: network_connection
    product: wireshark
detection:
    selection:
        protocol: c12.22
        length_field: "> 65535"
    condition: selection
falsepositives:
    - Legitimate C12.22 traffic with unusually long but valid message payloads (rare)
level: high

YARA Rule

rule CVE_2026_76886_C12_22_HeapOverflow {
    meta:
        author = "ValtersIT Threat Intelligence"
        description = "Detects PCAP files or packet captures containing malicious C12.22 traffic targeting the heap buffer overflow in Wireshark dissector (CVE-2026-76886)"
        date = "2026-05-15"
        cve = "CVE-2026-76886"
        severity = "high"
    strings:
        $c122_tag = { A0 43 02 12 22 }  // C12.22 application context identifier bytes (heuristic)
        $apdu_tag = { CD 00 00 00 }      // APDU structure tag marker
        $large_len16 = { FF FF }          // 16-bit length field at maximum value
        $large_len32 = { FF FF FF FF }    // 32-bit length field at maximum value
    condition:
        uint16(0) == 0x4D3C or  // PCAP magic number (little-endian)
        uint32(0) == 0x0A0D0D0A or  // PCAPNG magic
        ($c122_tag and ($large_len16 or $large_len32) and filesize < 10MB)
}

Note: The YARA strings for C12.22 protocol tags are heuristic and should be validated against actual C12.22 traffic captures to minimize false positives.

Suricata IDS Rule

alert ip any any -> any any (msg:"ET EXPLOIT Wireshark C12.22 Dissector Heap Overflow Attempt (CVE-2026-76886)"; flow:established,to_server; content:"|a0 43 02 12 22|"; offset:0; depth:5; content:"|ff ff|"; within:256; reference:cve,2026-76886; classtype:attempted-dos; sid:9000021; rev:1;)

Elastic Detection

// Elastic EQL query to detect packets flagged by the Wireshark dissector as malformed C12.22
// Requires packetbeat with protocol dissection enabled and event dataset set to packetbeat

sequence by source.ip
  [ network where network.protocol == "c12.22" and 
    network.transport == "tcp" and 
    event.action == "protocol_error" ]
  [ network where network.protocol == "c12.22" and 
    network.bytes > 50000 ]

Splunk SPL Query

index=network sourcetype=packetbeat OR sourcetype=tshark
| where like(protocol, "%c12.22%")
| eval oversized = if(len(payload) > 65535, 1, 0)
| search oversized=1
| stats count by src_ip, dest_ip, protocol, oversized
| where count > 0
| table _time, src_ip, dest_ip, protocol, count
| sort - count

Wazuh OSSEC Rule

<group name="wireshark,cve_2026_76886,dos,">
  <rule id="100786" level="10">
    <decoded_as>wireshark_log</decoded_as>
    <match>c12.22|C122</match>
    <description>CVE-2026-76886: C12.22 dissector heap overflow attempt detected in Wireshark logs</description>
    <group>cve_2026_76886,</group>
    <mitre>
      <id>T1499</id>
    </mitre>
  </rule>
</group>

Mitigation & Patch Guidance

Patch Confidence: 3/4 — LIKELY. Two independent sources (NVD and Debian Security Tracker) confirm that a fix is available, though the vendor has not yet published an official advisory at the time of this report.

1. Immediate Mitigations:

• Upgrade Wireshark to a patched version immediately. The fixed versions are 4.6.8 and 4.4.19 (or later). Verify the installed version with wireshark --version or tshark --version.
• For organizations that cannot immediately patch, apply the following interim measures:
  • Disable the C12.22 dissector: In Wireshark, navigate to Analyze → Display Filter Expressions → Protocols and disable C12.22. For tshark, add -d .c12.22==disable to command-line invocations.
  • Restrict Wireshark from automatically processing untrusted capture files by disabling "Enable dissector in packet list" options or configuring a strict display filter that excludes C12.22 ports (typically TCP/1153, port for C12.22 over TLS).
  • Implement a network-level filtering rule that drops or flags traffic destined for the C12.22 ports at the perimeter or on capture SPAN ports until patching is complete.

2. Patch/Upgrade Steps:

• Windows: Download the latest installer from the official Wireshark website and run the update.
• Debian/Ubuntu: Run sudo apt update && sudo apt upgrade wireshark (ensure you have the Debian security repository enabled).
• RPM-based distributions: Use sudo dnf update wireshark or sudo yum update wireshark.
• Verify the update: Confirm the installed version is ≥ 4.6.8 or ≥ 4.4.19.
• Validate that the C12.22 dissector no longer crashes by replaying the sample malicious PCAP through the patched version.

3. Long-Term Hardening:

• Establish a schedule for regular Wireshark updates — treat Wireshark as security-critical infrastructure, particularly in SOC and ICS monitoring environments.
• Implement endpoint memory protection mechanisms (ASLR, DEP) — most modern OS kernels enable these by default.
• Educate analysts against opening PCAP files from untrusted or unsolicited sources.
• For production capture pipelines, consider running tshark in a sandboxed environment or container with minimal privileges and a memory limit, so a crash does not impact the host.
• Subscribe to the Wireshark security advisories mailing list to receive CVE notifications promptly.

References

1. NVD Entry for CVE-2026-76886 — https://nvd.nist.gov/vuln/detail/CVE-2026-76886 — Official NVD record providing the description, CVSS vector, and CWE classification.
2. Debian Security Tracker — https://security-tracker.debian.org/tracker/CVE-2026-76886 — Confirms affected versions and patched package versions for Debian distributions.
3. Wireshark Official Site / Release Notes — https://www.wireshark.org/docs/relnotes/ — Release notes for Wireshark 4.6.8 and 4.4.19 that include the C12.22 dissector fix.
4. ANSI C12.22 Protocol Specification — https://www.nema.org/standards/view/ansi-c12-22 — Background on the C12.22 protocol for understanding the attack surface and affected industry context.

Threat Actor Campaign Evidence: No known active threat actor campaigns or in-the-wild exploitation have been documented for CVE-2026-76886 as of the publication date. The CISA KEV (Known Exploited Vulnerabilities) catalog does not list this CVE. The EPSS score of 0.00317 and its 23.9th percentile ranking of exploited CVEs suggest that, while a public PoC exists, the vulnerability has not yet been widely weaponized in real-world attacks. Monitoring for future CISA KEV inclusion is advised, as heap overflows in widely deployed analysis tools occasionally gain exploit traction.