CVE-2026-107171

Executive Summary

CVE-2026-107171 is a hardcoded cryptographic key vulnerability (CWE-321) in Trellix Agent version 5.8.4, specifically within the mfecryptc.dll component. An attacker with regular user access to a host running the affected agent can leverage the embedded key material to decrypt sensitive database contents that should otherwise be protected by the agent's encryption layer. This results in unauthorized disclosure of confidential data to any authenticated local user, with no elevated privileges required.

Technical Analysis

The vulnerability stems from a hardcoded cryptographic key embedded within the mfecryptc.dll library shipped with Trellix Agent 5.8.4. CWE-321 (Use of Hard-coded Cryptographic Key) describes a condition in which a cryptographic key — meant to provide confidentiality or integrity protection — is embedded directly in source code or a compiled binary rather than being generated per-installation or securely derived. Because the key is static across deployments of the same product version, it cannot be rotated without a code change and is recoverable by any party who can read the binary.

In this instance, the affected DLL (mfecryptc.dll) performs cryptographic operations that protect an agent-managed database. The description states that the hardcoded key "leads to Database Decryption by Regular Users," meaning the confidentiality protection of that database is effectively nullified against a local user with read access to the encrypted database file. The attack surface is local — an actor needs a foothold on a host running the Trellix Agent and the ability to read the encrypted database and the mfecryptc.dll binary. No network vector is required by the description; the flaw is exercised through local access.

From a cryptographic-design standpoint, a hardcoded key collapses the intended trust boundary. Because the value is identical on every installation of this version, an adversary who extracts it once can decrypt databases from any other host running the same agent version. This defeats the purpose of at-rest encryption and makes the protection essentially obfuscation rather than confidentiality. The exposure is deterministic: given the DLL and the ciphertext, decryption is a repeatable offline process, requiring no online oracle and producing no overt network traffic.

The precise key value, cipher mode, extraction technique, and database format are not disclosed in the available CVE description and are therefore intentionally omitted here; any statement of those specifics would be speculative. The technical claim that can be asserted from the source data is limited to: hardcoded key material in mfecryptc.dll in Trellix Agent 5.8.4 permits decryption of the associated database by a regular (non-administrative) Linux or Windows user with local access to the artifacts.

Exploitation Scenarios

No public proof-of-concept exists for this CVE, and the attack chain below is inferred from the vulnerability class (hardcoded cryptographic key) rather than from published exploit code. The following describes the exploit at the vulnerability-class level; specific function names, offsets, and parameters are not available and are not fabricated here.

1. Reconnaissance / target identification. The adversary obtains an initial low-privilege foothold on a host running Trellix Agent 5.8.4 (for example, via a separate initial-access vector, compromised credentials, or a malicious insider position). Because exploitation requires only regular-user rights, no privilege escalation is a prerequisite. The actor enumerates installed security agents and confirms the presence and version of mfecryptc.dll in the agent install directory.

2. Triggering the flaw class. The actor reads the encrypted database file produced/consumed by the agent and the mfecryptc.dll binary. Because the cryptographic key is hardcoded into the DLL, it is recoverable from the binary by offline static analysis — no running process, debugger, or elevation is strictly required. The design intent of at-rest protection is defeated the moment the DLL is readable.

3. Payload / execution method. Using the extracted static key and the relevant cipher parameters (inferred from the DLL), the actor decrypts the database offline on their own system or on the compromised host using standard cryptographic tooling. This is a purely local, offline decryption step; it generates no distinctive network signature, which is precisely why detection must focus on file-access and process behavior rather than network traffic.

4. Post-exploitation impact. The decrypted database exposes confidential information that the encryption layer was meant to protect. Depending on what the agent stores, this could include operational telemetry, configuration, or credential-adjacent material. Disclosure is the primary impact; there is no described path to code execution or data modification from this flaw alone. Because the key is shared across all installations of version 5.8.4, an actor who extracts the key once can reuse it against every other vulnerable host they encounter, amplifying the blast radius beyond a single compromised endpoint.

Impact Assessment

The primary impact is confidentiality loss (CWE-321 class), scored as High for confidentiality under the provided conceptual vector. Integrity and availability are not described as affected by the flaw itself. The required privilege level is Low (regular user) and no user interaction is needed beyond the initial foothold. Attack complexity is Low — static key extraction and offline decryption are well-understood techniques requiring commodity tooling. The affected system scope is Unchanged.

Business impact: organizations that rely on Trellix Agent's at-rest encryption to protect locally stored database contents should treat that data as effectively plaintext to any local user on a vulnerable host. In regulated environments, exposure of agent-managed data could constitute a reportable data-disclosure event. The shared-key nature means a single successful extraction has fleet-wide implications for all endpoints at version 5.8.4, making the aggregate blast radius substantially larger than one host. EPSS is 0.00122 (1.8th percentile), indicating low near-term exploitation likelihood based on current evidence; there is no CISA KEV listing, no public PoC, and no Nuclei template at the time of writing. The absence of observed exploitation does not reduce the structural severity, since no elevated privileges or network exposure are required.

Detection Guidance

Sigma Rule

title: Suspicious Access to Trellix Agent mfecryptc.dll and Encrypted Database
id: 3f7a9c21-0b4e-4d6a-9c11-7e2b1a5d8f30
status: experimental
description: Detects non-Trellix processes reading the mfecryptc.dll module or the agent-managed encrypted database, consistent with hardcoded-key extraction/decryption (CVE-2026-107171)
references:
  - https://nvd.nist.gov/vuln/detail/CVE-2026-107171
author: valtersit.com
date: 2026/01/01
logsource:
  category: file_access
  product: windows
detection:
  selection_dll:
    TargetFilename|endswith: '\mfecryptc.dll'
  selection_db:
    TargetFilename|contains: 'Trellix'
    TargetFilename|endswith: '.db'
  filter_agent:
    Image|contains: 'Trellix'
  condition: (selection_dll or selection_db) and not filter_agent
fields:
  - Image
  - TargetFilename
  - User
falsepositives:
  - Legitimate Trellix maintenance or upgrade operations
level: medium

YARA Rule

rule CVE_2026_107171_Hardcoded_Key_mfecryptc
{
    meta:
        description = "Detects mfecryptc.dll associated with hardcoded cryptographic key in Trellix Agent 5.8.4"
        author = "valtersit.com"
        reference = "https://nvd.nist.gov/vuln/detail/CVE-2026-107171"
        cve = "CVE-2026-107171"
        date = "2026-01-01"

    strings:
        $dll = "mfecryptc" ascii wide nocase
        $agent = "Trellix Agent" ascii wide nocase
        $ver = "5.8.4" ascii wide

    condition:
        uint16(0) == 0x5A4D and filesize < 20MB and
        ($dll or $agent) and $ver
}

Suricata IDS Rule

alert http any any -> any any (msg:"CVE-2026-107171 Trellix Agent mfecryptc.dll Reference in HTTP"; flow:established,to_server; http.uri; content:"mfecryptc"; nocase; http.header; content:"Trellix"; nocase; classtype:attempted-recon; sid:2026107171; rev:1; metadata:created_at 2026_01_01, cve CVE-2026-107171;)

Elastic Detection

file where process.name != null and
  file.name : "mfecryptc.dll" and
  not process.name : ("Trellix*" or "mcafee*" or "TrellixAgent*")

Splunk SPL Query

index=endpoint (EventCode=11 OR EventCode=4663)
| search (TargetFilename="*mfecryptc.dll*" OR (TargetFilename="*Trellix*.db" OR TargetFilename="*.mdb*"))
| where NOT match(Image, "(?i)Trellix|mcafee|TrellixAgent")
| stats count min(_time) as first_seen max(_time) as last_seen values(TargetFilename) as files values(User) as users by host Image
| sort - count

Wazuh OSSEC Rule

<group name="trellix,cve-2026-107171,">
  <rule id="107171" level="8">
    <if_sid>550</if_sid>
    <field name="file">mfecryptc\.dll$</field>
    <description>CVE-2026-107171: Possible access to Trellix Agent mfecryptc.dll by non-agent process</description>
    <mitre>
      <id>T1552</id>
    </mitre>
  </rule>
  <rule id="107172" level="8">
    <if_sid>550</if_sid>
    <field name="file">Trellix.*\.db$</field>
    <description>CVE-2026-107171: Possible access to Trellix Agent encrypted database</description>
  </rule>
</group>

Mitigation & Patch Guidance

Patch confidence: 0/4 (UNPATCHED — no patch evidence from any tracked source). No vendor fix, workaround, or affected-version range was supplied by any tracked source.

1. Immediate mitigations.

   • Restrict read access to the Trellix Agent installation directory, and in particular to mfecryptc.dll and the associated encrypted database, to the minimum set of service accounts and administrators required for operation. Where the OS permits, remove regular-user read permission from these artifacts.
   • Treat any data protected solely by the affected agent's encryption as non-confidential while the host remains on an unpatched version, and adjust data-handling and retention decisions accordingly.
   • Monitor for unauthorized copies, reads, or exfiltration of the DLL and database files (see Detection Guidance) as an early indicator of key extraction.
   • Isolate high-value endpoints that store sensitive agent-managed data until a fix is available.

2. Patch / upgrade steps.

   • There is currently no patched version identified by tracked sources. Monitor the Trellix security advisory channel and the NVD entry for CVE-2026-107171 for a fixed release.
   • When a fixed Trellix Agent version is published, upgrade all endpoints at 5.8.4. Because the key is hardcoded and shared across the version, upgrading is necessary on every host — remediating a subset leaves the fleet exposed.
   • After upgrading, verify that any databases encrypted with the vulnerable static key are re-encrypted under the new scheme, and rotate any secrets that may have been exposed through prior decryption.

3. Long-term hardening.

   • Require vendors to derive encryption keys per-installation (for example, from a hardware-backed keystore or an OS-protected secret store) rather than shipping static keys in binaries; include this as an explicit procurement and security-review criterion.
   • Implement application control and file-integrity monitoring on security-agent binaries to detect tampering or unusual access patterns.
   • Maintain an inventory of security agents and their versions so that exposure to agent-specific CVEs can be assessed fleet-wide quickly.

References

• NVD — CVE-2026-107171: https://nvd.nist.gov/vuln/detail/CVE-2026-107171
• CWE-321 — Use of Hard-coded Cryptographic Key: https://cwe.mitre.org/data/definitions/321.html
• MITRE ATT&CK T1552 — Unsecured Credentials: https://attack.mitre.org/techniques/T1552/
• Trellix Security Advisories (vendor advisory channel): https://www.trellix.com/en-us/about/newsroom/security-advisories/
• CISA Known Exploited Vulnerabilities Catalog (CVE-2026-107171 not listed at time of writing): https://www.cisa.gov/known-exploited-vulnerabilities-catalog

No public exploit code, PoC, Nuclei template, or in-the-wild campaign has been identified for this CVE at the time of writing. EPSS is 0.00122 (1.8th percentile). CISA KEV status: not listed.