Critical Improper Input Validation in Exim MTA (CVE‑2019‑10149) Enables Remote Command Execution
What It Is
CVE‑2019‑10149 is a flaw in the Exim Mail Transfer Agent’s deliver_message() routine. The function fails to properly validate the recipient address supplied to /src/deliver.c, allowing an attacker to inject arbitrary command strings that the MTA will execute on the host.
Exploitability
The vulnerability is rated Critical (CVSS ≥ 9.0) and is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. Public proof‑of‑concept code exists, and multiple threat‑intel feeds have documented active exploitation against Internet‑facing Exim instances.
Affected Products
- Vendor: Exim
- Product: Exim Mail Transfer Agent (any version prior to the patched release that includes the fix for CVE‑2019‑10149)
Why It Matters for Compliance & Audit Readiness
Improper input validation in a core email service undermines the access‑control and system‑integrity domains of most regulatory frameworks (e.g., NIST CSF, ISO 27001). Evidence of timely patch management and continuous control monitoring around mail‑server configurations is a key audit artifact for demonstrating due diligence. Mapping this vulnerability to the “Secure Configuration Management” control helps organizations prove that they maintain a defensible posture against remote code execution vectors.
Recommended Actions
- Map the control: Align the Exim patch to the “Configuration Management” control in your security framework.
- Capture evidence: Document the patch version, deployment date, and verification logs in your configuration‑management database (CMDB).
- Validate posture: Run an authenticated scan of all mail servers to confirm the vulnerable code path is remediated.
- Monitor for abuse: Enable logging of recipient address parsing and set alerts for anomalous command‑injection patterns.
Source: https://nvd.nist.gov/vuln/detail/CVE-2019-10149