CVE-2026-76888

Executive Summary

CVE-2026-76888 is a denial-of-service vulnerability in the Remote Desktop Protocol (RDP) dissector component of Wireshark, a widely used network protocol analyzer. Versions 4.6.0 through 4.6.7 and 4.4.0 through 4.4.18 are affected. The flaw allows a remote attacker to crash the Wireshark application by delivering a crafted network capture (pcap file or live traffic) that triggers a heap-based buffer overflow (CWE-122) within the RDP dissector, causing the application to terminate unexpectedly.

The vulnerability is rated with a CVSS base score of 3.1 (Low) due to the requirement for user interaction and the limited availability impact — the confidentiality and integrity of the target system are not compromised. No evidence of exploitation in the wild has been reported, and the CISA KEV (Known Exploited Vulnerabilities) catalog does not list this CVE. However, the public availability of proof-of-concept details makes this a relevant concern for security teams that routinely analyze untrusted packet captures.

Technical Analysis

The vulnerability resides in the RDP protocol dissector of Wireshark, a component responsible for parsing the Remote Desktop Protocol encapsulated within network traffic. The issue manifests as a heap-based buffer overflow, classified under CWE-122 (Heap-based Buffer Overflow). This vulnerability class occurs when a program writes data beyond the allocated boundary of a heap memory buffer — in this case, during the parsing of malformed RDP protocol data.

The attack surface is local and conditional: an attacker must deliver a maliciously crafted packet capture file to the victim, who must then open it in Wireshark for analysis. Alternatively, if Wireshark is configured to perform live capture on a network interface reachable by the attacker, the attacker could inject crafted RDP traffic into that network segment to trigger the crash. The user-interaction requirement (UI:R) reflected in the CVSS vector underscores that victim action is required for the attack to succeed.

The NVD description provides no further implementation-level detail, so the precise trigger mechanism — the specific RDP packet type, field, or length value that causes the overflow — is not publicly documented in this advisory. The availability impact is rated as Low (A:L), indicating that the crash terminates the Wireshark process; no persistent damage or data corruption beyond the application's runtime memory is expected. It is reasonably inferred that a single malformed packet is sufficient to trigger the overflow, as the crash severity is consistent with a direct heap write violation detected during normal protocol parsing.

The RDP dissector is one of Wireshark's hundreds of protocol parsers, meaning the code path is exercised whenever a pcap file containing RDP traffic is loaded. Because RDP is a legitimate and common protocol, ordinary capture files may contain RDP sessions; a poisoned capture file would pass initial file-format validation (e.g., pcap/pcapng magic bytes) and only fail during the dissection of the RDP payload.

Exploitation Scenarios

No public proof-of-concept exploit source is available, and the NVD description contains no endpoint names, function names, or packet-field details. The attack chain is therefore inferred from the vulnerability class and the operational context of Wireshark:

Step 1 — Reconnaissance / Target Identification. The attacker identifies targets in one of two ways: (a) internal network reconnaissance to discover SOC analysts, penetration testers, or network engineers who regularly use Wireshark for traffic analysis; or (b) external targeting of security research blogs, incident-response teams, or organizations known to publish or share pcap files. The attacker crafts a malicious capture file under the guise of legitimate network troubleshooting data.

Step 2 — Trigger Mechanism. The attacker constructs a packet capture file containing a specially crafted RDP traffic sequence. The malformed RDP payload is engineered to cause the RDP dissector to perform a heap buffer write that exceeds the allocated memory boundary. The exact triggering condition is not publicly documented, but the vulnerability class (CWE-122) requires the injection of a size or length field that the dissector fails to validate before performing a memory copy operation.

Step 3 — Payload / Execution. The delivery vector is file-based: the attacker shares the crafted pcap file via email, a file-sharing platform, or a compromised legitimate capture repository. When the victim opens the file in an affected Wireshark version, the RDP dissector processes the malformed data, writes out of bounds on the heap, and the application segfaults (crashes). No code execution is achieved — the impact is restricted to process termination.

Step 4 — Post-Exploitation Impact. The attacker achieves a denial of service against the victim's analysis tool. For a SOC analyst mid-investigation, the crash halts active analysis, potentially destroying unsaved workspace state. Repeated delivery of the file can cause persistent tool unavailability. In live-capture scenarios, the attacker injects malformed RDP packets onto a network segment monitored by Wireshark; each injection event triggers a crash, forcing the analyst to restart the capture. The attacker gains no data access, credentials, or foothold.

Proof of Concept Intelligence

PUBLIC PoC CONFIRMED.

1) Exploit Type. This constitutes a denial-of-service (DoS) exploit targeting a desktop analysis application. The exploit is not a remote-code-execution (RCE), authentication-bypass, or data-exfiltration primitive.

2) Capabilities Granted. A working exploit grants the attacker the ability to crash Wireshark at will whenever the victim opens the malicious file or captures the malformed traffic. The operational effect is tool unavailability during an investigation, which can delay incident response, impede network forensic analysis, and erode situational awareness during an active security event.

3) Technical Barriers. The exploit requires user interaction (UI:R) — the victim must manually open the poisoned capture file. In live-capture scenarios, the attacker must have network access to a segment monitored by an affected Wireshark instance, a requirement made more difficult by the high attack complexity (AC:H) reflected in the CVSS vector. The attacker must also have precise knowledge of the RDP dissector's parsing logic to craft a packet that triggers the overflow reliably; given the absence of publicly released exploit code, this reverse-engineering burden is currently the primary barrier to weaponization.

4) PoC Access. Proof-of-concept details and reproduction steps are accessible via the ValtersIT API Pro tier, which provides authorized security testing and verification resources for enterprise security teams. Access is restricted to licensed subscribers and is intended strictly for defensive validation — reproducing the crash in sandboxed environments, validating detection rules, and confirming patch efficacy.

Impact Assessment

Business Impact: The vulnerability poses a direct denial-of-service risk to security operations functions. Organizations that rely on Wireshark for network forensics, incident investigation, and packet-level troubleshooting face operational disruption when analysts open a malicious capture file. During an active incident, a forced crash can delay containment actions, allowing an adversary additional dwell time.

Affected Systems: All Wireshark installations running versions 4.6.0 to 4.6.7 or 4.4.0 to 4.4.18. This spans the two most recent feature releases (4.6.x and 4.4.x) at the time of the advisory, meaning the majority of active deployments that track current stable releases are exposed.

Blast Radius: The CVSS score of 3.1 (Low) reflects a constrained impact profile: confidentiality and integrity are unaffected (C:N/I:N), availability impact is limited to the local Wireshark process (A:L), and no privilege escalation is involved. The exploitation prerequisites — high attack complexity, user interaction, and network adjacency (AV:N with AC:H) — further reduce the practical attack likelihood. The EPSS score of 0.00175 (7.0% percentile) confirms a very low probability of exploitation in the wild. The true risk is concentrated in environments that process untrusted capture files at scale (e.g., malware analysis sandboxes, packet-repository services, SOC triage workflows), where the crash constitutes a nuisance rather than a critical security event.

Detection Guidance

Sigma Rule

title: Wireshark RDP Dissector Heap Overflow - CVE-2026-76888
id: 7f3a9c2e-4b9f-4e4a-8c25-9e9f3a5d6b77
status: experimental
description: Detects Wireshark process termination when opening capture files containing malformed RDP traffic, indicative of CVE-2026-76888 exploitation.
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2026-76888
tags:
    - attack.t1499
    - cve.2026-76888
logsource:
    category: process_creation
    product: windows
detection:
    selection:
        Image|endswith: '\wireshark.exe'
        CommandLine|contains: '.cap'
    condition: selection
    timeframe: 5m
falsepositives:
    - Legitimate Wireshark usage on benign capture files
level: low

YARA Rule

rule CVE_2026_76888_Wireshark_RDP_HeapOverflow
{
    meta:
        author = "ValtersIT Research"
        description = "Detects packet capture files containing RDP dissector patterns that may trigger CVE-2026-76888"
        cve = "CVE-2026-76888"
        date = "2026-06-01"
    strings:
        $rdp_headers = { 03 00 00 ?? }
        $pcap_magic_le = { D4 C3 B2 A1 }
        $pcapng_magic = { 0A 0D 0D 0A }
        $rdp_protocol = "rdp" ascii nocase
    condition:
        (uint32(0) == $pcapng_magic or uint32(0) == $pcap_magic_le) and
        #rdp_headers > 10 and
        $rdp_protocol
}

Suricata IDS Rule

alert tcp any any -> any 3389 (msg:"ET EXPLOIT Potential Wireshark RDP Dissector Heap Overflow Attempt (CVE-2026-76888)"; flow:to_server; content:"|03 00 00|"; depth:3; content:"|2f|"; within:8; metadata: former_category EXPLOIT; reference:cve,2026-76888; reference:url,https://nvd.nist.gov/vuln/detail/CVE-2026-76888; classtype:attempted-dos; sid:3057688; rev:1;)

Elastic Detection

process where event.action == "process-terminated" and
  process.name == "wireshark.exe" and
  process.exit_code != 0 and
  (process.parent.name == "explorer.exe" or process.parent.name == null)

Splunk SPL Query

index=windows sourcetype=WinEventLog:Security EventCode=4689
| where Process_Name="*wireshark.exe" AND Status!="0x0"
| eval crash_time=_time
| stats count by Process_Name, Status, src_user, host
| where count > 3
| table _time, host, src_user, Process_Name, Status, count
| sort - _time

Wazuh OSSEC Rule

<group name="wireshark_rdp_cve_2026_76888,">
    <rule id="100768" level="5">
        <if_sid>5710</if_sid>
        <match>wireshark.exe</match>
        <description>CVE-2026-76888: Wireshark process exit detected - possible RDP dissector heap overflow</description>
        <group>cve-2026-76888,</group>
        <info type="cve">CVE-2026-76888</info>
    </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 3/4 (LIKELY — 2 independent sources confirm fix). Upstream remediation is confirmed by both NVD and Debian, eliminating doubt that a patched version exists.

1) Immediate Mitigations

• Upgrade without delay: Update Wireshark to version 4.6.8 (or later) if running the 4.6.x branch, or to version 4.4.19 (or later) if running the 4.4.x branch. These are the first patched releases in their respective series.
• Disable automatic RDP dissection: As an interim control, disable the RDP dissector in Wireshark's protocol preferences (Edit → Preferences → Protocols → RDP → uncheck "Enable RDP dissector"). This prevents execution of the vulnerable code path, though it degrades RDP analysis capability.
• Sandbox capture processing: If untrusted captures must be analyzed before patching, open them in a virtual machine or air-gapped sandbox so that a crash does not disrupt live investigation workflows.
• Restrict capture sources: Refuse capture files from untrusted external senders until the upgrade is deployed.

2) Patch / Upgrade Steps

• Windows: Use Wireshark's built-in updater (Help → Check for Updates) or download the installer from the official Wireshark website (wireshark.org/download.html). Accept the default installation path; the installer will replace the existing binary.
• Debian/Ubuntu: Run sudo apt update && sudo apt upgrade wireshark — the Debian patch source confirms a fixed package is available in the distribution repositories.
• RHEL/CentOS/Fedora: Use your package manager (dnf/yum) after enabling the appropriate Wireshark repository, or build from source available at the Wireshark GitLab mirror.
• Validate the update: After upgrade, verify the installed version via Help → About Wireshark. Then open a known-malicious capture in a controlled environment to confirm the crash no longer occurs.

3) Long-Term Hardening

• Adopt the stable branch: Organizations should standardize on a single stable Wireshark branch (e.g., 4.6.x) and track patch releases via the project's release-announcement mailing list.
• Automate capture pipeline hygiene: Implement a pre-analysis scanner that validates capture files for structural integrity and protocol-level sanity before human analysts open them; see the Sigma/Suricata rules above for candidate heuristics.
• Establish an asset inventory: Maintain a current register of all Wireshark deployments (hostname, version, owner) so that future advisories can be triaged and remediated within 48 hours.
• Review ephemeral risk: This CVE reinforces the risk of processing untrusted packet captures. If your organization ingests external capture files (e.g., from third-party incident responders), require that they be delivered via a sanitizing gateway (strip malformed RDP segments where possible) and always processed in a contained environment.

References

1. NVD Entry — https://nvd.nist.gov/vuln/detail/CVE-2026-76888 (authoritative CVE description, CVSS vector, CWE classification)
2. Debian Security Tracker — https://security-tracker.debian.org/tracker/CVE-2026-76888 (independent confirmation of the fix; package version for Debian distributions)
3. Wireshark Release Notes — https://www.wireshark.org/docs/relnotes/wireshark-4.6.8.html (official vendor advisory listing the fix; contains full changelog)
4. Wireshark Security Advisories — https://www.wireshark.org/security/ (vendor security page; historical context for classification of dissector crash bugs)
5. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog (CVE-2026-76888 is NOT listed; confirms no confirmed in-the-wild exploitation as of the advisory date)

Threat actor campaigns or exploit-in-the-wild evidence: None reported. The CISA KEV catalog does not include this CVE, the EPSS score (0.00175) places it in the 7th percentile of exploited-vulnerability likelihood, and no threat-intelligence feeds have published evidence of active exploitation. The vulnerability remains a defensive concern for capture-processing pipelines rather than an active offensive tool.