CVE-2026-18751

CVE-2026-18751 — Threat Intelligence Report

Executive Summary

CVE-2026-18751 is an external control of file name or path vulnerability (CWE-73) in Citrix Workspace App for macOS, affecting build 2607. An attacker who can influence the application's file-handling logic could cause the client to read from or write to unintended locations on the host file system, potentially enabling arbitrary file write, sensitive data disclosure, and ultimately local code execution or persistence. As of this report, no official patch exists, the CVE is not listed in CISA's Known Exploited Vulnerabilities catalog, and no public proof-of-concept or in-the-wild exploitation has been reported.

Technical Analysis

CWE-73 (External Control of File Name or Path) is a path-control vulnerability class where software uses externally supplied input to construct a file name or path that should be restricted to a specific directory, but does not properly neutralize special elements such as ../ traversal sequences or absolute path components. The NVD description for CVE-2026-18751 is sparse: it identifies only the product (Citrix Workspace App on macOS), the affected build (2607), and the vulnerability class. No function names, API endpoints, specific file paths, or code-level details are provided in the advisory, so the technical analysis below is performed at the vulnerability-class level rather than from observed implementation specifics.

Citrix Workspace App is an endpoint client used by enterprises to broker access to virtual desktops, published applications, and software-as-a-service resources. As a session-brokering client, the application routinely processes externally supplied data — including server-provided workspace configuration, session launch files, and downloaded content — and frequently performs file read/write operations for caching, configuration, and session management. Any code path that concatenates external input with a base directory to compute a target path is a candidate attack surface for CWE-73. If an attacker can inject traversal sequences or absolute path components into that concatenation, the application may escape its intended working directory.

The attack surface is meaningful because the client runs on the user's macOS workstation and typically operates with the user's privileges. An unchecked path-control flaw in such a client means that a malicious input source (for example, a task that induces the user to open a crafted profile or session file, or a server response altered in transit) can turn the trusted enterprise client into an arbitrary file read/write primitive on the host. This is particularly relevant on macOS, where user-writable directories such as launch-agent directories, application support folders, and dynamic library search paths are common targets for persistence or code-injection techniques. An arbitrary file read could similarly expose local credentials, cached authentication tokens, or sensitive workspace data.

No additional affected versions are listed in the advisory, and the structured NVD fields record the vendor as "Unknown" even though the description text explicitly attributes the product to Citrix. The absence of a CVSS vector, EPSS score, and CISA KEV inclusion means there is no independently verified severity rating or exploitation evidence at this time.

Exploitation Scenarios

No public PoC or exploit code is available for CVE-2026-18751. The attack chain below is inferred from the vulnerability class and the known product context, not from observed implementation details.

1. Reconnaissance / target identification. An attacker identifies macOS endpoints running Citrix Workspace App build 2607. This can be done by enumerating installed software versions on already-compromised hosts, by querying the client's update or version metadata, or by social-engineering a user into revealing their client version. In a targeted scenario, the attacker may first compromise a separate low-privilege foothold on the endpoint and then use this flaw to escalate impact.

2. Triggering the specific flaw class. CWE-73 is triggered when the application builds a file path from untrusted input without sanitization. In a Citrix Workspace context, candidate untrusted input channels include session configuration files (e.g., ICA session files), data fetched from a malicious or man-in-the-middled gateway/server, or any downloaded artifact the client processes before performing a file operation. The crafted input is expected to include path traversal elements (../) or absolute path components that the vulnerable build 2607 fails to neutralize.

3. Payload / execution method. Because the vulnerability is a path-control flaw, the "payload" is the destination or source path chosen by the attacker. For an arbitrary file write, the attacker directs the application to write a file outside its intended directory — for example, into a macOS startup or launch-agent location — so that the content is later loaded or executed. For an arbitrary file read, the attacker causes the application to read a sensitive local file and either display it, cache it, or transmit it to a location the attacker can access. Insufficient technical detail is available to name the specific routines that perform these operations.

4. Post-exploitation impact. Successful exploitation can yield persistence on the host, theft of credentials or tokens cached by the Workspace client, or execution of attacker-supplied content. If the vulnerable client runs in an elevated context in some enterprise configurations, the flaw could also serve as a local privilege escalation primitive. Post-exploitation, an attacker with code execution on the endpoint can pivot to the enterprise resources reachable through the Citrix session.

Impact Assessment

Business impact. Citrix Workspace is a trusted client that provides access to enterprise virtual desktops and internal applications. A path-control vulnerability in the macOS client means that a malicious input source can turn that trusted client into a local file read/write primitive. This jeopardizes the confidentiality of data stored on the endpoint (credentials, tokens, cached sessions) and the integrity of the endpoint itself (persistence, configuration tampering). In environments where Workspace is the primary access path to corporate resources, a compromised client can become a pivot point into the internal network.

Affected systems. Apple macOS hosts running Citrix Workspace App build 2607. The advisory lists only this exact build; no version range or additional affected builds are confirmed. Because the affected version field in the structured data is empty, the true scope may be broader and should be monitored as the vendor investigates.

Blast radius. Endpoint-only at this time — the NVD description does not indicate any server-side component. However, Citrix Workspace clients are ubiquitous in enterprise VDI deployments, so the blast radius across a single organization could encompass every macOS user who has installed the affected build.

Severity reference. The CNA/NVD has not assigned a CVSS vector (CVSS: N/A), so no official severity score exists. FIRST has not yet scored the CVE for EPSS. The CISA KEV catalog does not include CVE-2026-18751, meaning there is no authoritative public evidence of exploitation in the wild. PoC/exploit status is unknown, with no Nuclei template and no published exploit code.

Detection Guidance

Detection for this vulnerability is primarily host-based. File event telemetry, file integrity monitoring (FIM), process audit logs, and endpoint detection and response (EDR) data are the most reliable sources for identifying anomalous path traversal activity by the Citrix Workspace process. The rules below are realistic templates that SOC teams should adapt to their specific log schemas.

Sigma Rule

title: Citrix Workspace App Suspicious Path Traversal on macOS
id: 8a2e6f14-8c3b-4f2a-9d61-7b19e0c4a2f1
status: experimental
description: >
  Detects file read/write events by Citrix Workspace App on macOS that contain
  path traversal sequences or attempts to access system directories, which may
  indicate exploitation of CVE-2026-18751 (CWE-73).
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-18751
author: ValtersIT Threat Intelligence
date: 2026-01-15
logsource:
  category: file_event
  product: macos
detection:
  selection_traversal:
    Image|contains: 'Citrix Workspace'
    TargetFilename|contains:
      - '\..\'
      - '..%2f'
      - '%2e%2e'
  selection_system_paths:
    Image|contains: 'Citrix Workspace'
    TargetFilename|startswith:
      - '/etc/'
      - '/usr/'
      - '/var/root/'
      - '/Library/LaunchDaemons/'
  condition: selection_traversal or selection_system_paths
falsepositives:
  - Some legitimate Citrix features may reference absolute paths for configuration.
level: high

YARA Rule

rule CVE_2026_18751_Citrix_Workspace_PathTraversal
{
    meta:
        author = "ValtersIT Threat Intelligence"
        description = "Detects crafted Citrix Workspace input files containing path traversal payloads associated with CVE-2026-18751"
        cve = "CVE-2026-18751"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-18751"
        date = "2026-01-15"

    strings:
        $traversal1 = "../" ascii
        $traversal2 = "..\\" ascii
        $traversal3 = "%2e%2e%2f" ascii
        $traversal4 = "%2e%2e%5c" ascii
        $dotdot = ".." ascii

    condition:
        filesize < 5MB
        and 2 of ($traversal*)
        and $dotdot
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-18751 Citrix Workspace Path Traversal Attempt";
    flow:established,to_server;
    content:"GET"; http_method;
    content:"%2e%2e%2f"; http_uri; nocase;
    classtype:attempted-admin;
    sid:202618751; rev:1;)

Note: The ICA/session protocol used by Citrix Workspace frequently travels over HTTP(S) to gateways and storefront servers. Once the specific transport or vulnerable message type is disclosed by the vendor, additional Suricata rules should be created for that protocol. The rule above detects common URL-encoded traversal patterns in the client traffic.

Elastic Detection

file where
  process.name : "*Citrix*" and
  (
    file.path : "*..*" or
    file.path : "/etc/*" or
    file.path : "/usr/*" or
    file.path : "/Library/LaunchDaemons/*"
  ) and
  not file.extension : ("log", "tmp", "cache")

Splunk SPL Query

index=endpoint sonly=macos OR sourcetype=*macos*
  (process="*Citrix*" OR process_name="*Citrix*")
  (file_path="*../*" OR file_path="*%2e%2e*" OR file_path="*..\\*"
   OR file_path="/etc/*" OR file_path="/usr/*" OR file_path="/Library/LaunchDaemons/*")
| eval cve="CVE-2026-18751"
| table _time, host, user, process, process_name, file_path, file_name, action
| sort - _time

Wazuh OSSEC Rule

<group name="cve-2026-18751,">
  <rule id="100261" level="12">
    <if_sid>550</if_sid>
    <field name="file">\.\.</field>
    <match>citrix workspace</match>
    <description>CVE-2026-18751: Citrix Workspace App path traversal attempt detected</description>
  </rule>
</group>

Note: Adjust the parent rule ID (550 is the generic auditd syscall rule) to match your Wazuh environment's FIM or auditd log source. If the environment lacks process-level visibility for file events, pair the rule with a broader FIM alert on the application's installation and configuration directories.

Mitigation & Patch Guidance

Patch confidence: 0/4 — UNPATCHED. No patch evidence from any tracked source, and no vendor fix is currently available. The following steps are recommended.

1. Immediate mitigations

   • Inventory all macOS endpoints running Citrix Workspace App build 2607 and flag them for accelerated patching once a fixed build is released.
   • Restrict users from opening untrusted session/profile files and block untrusted network paths to the Workspace client where the enterprise architecture allows it.
   • Enable file-integrity monitoring and EDR alerting on the directories used by the application.
   • Apply the principle of least privilege; run the client with standard user rights rather than administrative rights.

2. Patch / upgrade steps

   • Monitor Citrix Security Bulletins and the NVD entry for CVE-2026-18751, and subscribe to vendor alerts so that the fix is deployed as soon as it is published.
   • When a fixed build is released, upgrade all affected macOS clients, verify the build hash before deployment, and re-run the detection queries above to confirm no prior compromise.
   • Confirm with Citrix support whether downgrading to a pre-2607 build is a supported interim option for high-risk environments.

3. Long-term hardening

   • Adopt a managed update strategy for endpoint clients so security fixes are deployed quickly.
   • Harden the local host with application allowlisting and EDR that monitors file-write events from network-connected client processes.
   • Segment the network so endpoint clients reach Citrix infrastructure only through authenticated, inspected channels.
   • Include CWE-73 testing in internal code reviews and vendor-supplier audits for similar desktop clients.

References

1. NVD Entry for CVE-2026-18751 — https://nvd.nist.gov/vuln/detail/CVE-2026-18751
2. MITRE CVE Record — https://www.cve.org/CVERecord?id=CVE-2026-18751
3. CWE-73: External Control of File Name or Path — https://cwe.mitre.org/data/definitions/73.html
4. Citrix Security Bulletins — https://support.citrix.com/securitybulletins (monitor for forthcoming vendor advisory)
5. CISA Known Exploited Vulnerabilities Catalog — https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No known threat actor campaigns or exploit-in-the-wild evidence has been identified for CVE-2026-18751 as of the report date. The CISA KEV catalog does not currently include this CVE.