CVE-2026-66140 in Exim
Summary
by MITRE • 07/24/2026
Exim before 4.99.5 allows directory traversal to access files outside of the spool area, and consequently gain privileges, because arguments related to queue-name are mishandled.
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Analysis
by VulDB Data Team • 07/24/2026
This vulnerability exists in Exim versions prior to 4.99.5 and represents a critical directory traversal flaw that enables unauthorized file access beyond the intended spool area boundaries. The vulnerability stems from improper handling of queue-name arguments within the email processing pipeline, allowing malicious actors to manipulate path resolution mechanisms and access arbitrary files on the system. The flaw specifically affects the queue management functionality where queue names are processed without adequate input validation or sanitization measures. Attackers can exploit this weakness by crafting specially formatted queue names that traverse directory structures using sequences like ../ or similar path manipulation techniques. This vulnerability directly maps to CWE-22 Path Traversal and CWE-73 Path Traversal in the Common Weakness Enumeration framework, which categorizes it as a privilege escalation vector through unauthorized file access.
The operational impact of this vulnerability extends beyond simple information disclosure to encompass full system compromise potential. An attacker who successfully exploits this directory traversal flaw can access sensitive configuration files, authentication credentials, and potentially gain elevated privileges depending on the system's permission model. The spool area typically contains email messages and associated metadata that may include sensitive communications or system information. When combined with other vulnerabilities or misconfigurations, this flaw could enable attackers to escalate privileges by accessing system files or binaries with higher permissions. The vulnerability affects systems where Exim operates with elevated privileges during queue processing operations, making the attack surface particularly dangerous in multi-tenant environments or systems handling confidential email traffic.
Mitigation strategies should prioritize immediate patching of affected Exim installations to version 4.99.5 or later, which contains proper input validation and path sanitization mechanisms for queue-name arguments. Organizations should implement strict input validation policies that sanitize all user-supplied data before processing, particularly in contexts involving file system operations or path resolution. Network segmentation and access controls should limit exposure of Exim services to trusted networks only, reducing the attack surface available to potential exploiters. System administrators should conduct comprehensive audits of Exim configurations to ensure proper spool directory permissions and implement monitoring solutions that detect unusual file access patterns or path traversal attempts. The mitigation approach aligns with ATT&CK technique T1059 Command and Scripting Interpreter and T1566 Phishing, as attackers typically leverage such vulnerabilities during initial compromise phases to establish persistent access. Regular security assessments should include testing for similar directory traversal vulnerabilities in other mail transfer agents and system components that process user-supplied paths or filenames.