CVE-2026-55618 in eml_parser
Summary
by MITRE • 08/25/2026
eml_parser serves as a python module for parsing eml files and returning various information found in the e-mail as well as computed information. Prior to 3.0.2, the clean_found_uri function in eml_parser/parser.py validates potential URL strings before unescaping HTML entities used for colon, slash, or period characters. Valid encoded URLs and their host names are therefore rejected and omitted from the extracted URL and domain lists. Email security gateways and SOC pipelines that use those lists as indicators of compromise may fail to submit the hidden URLs to threat intelligence feeds, reputation services, or sandboxes, allowing malicious links to bypass inspection. This issue is fixed in version 3.0.2.
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Analysis
by VulDB Data Team • 08/25/2026
The eml_parser module functions as a critical utility for extracting and analyzing data from Electronic Mail Message Format files, providing both raw information and computed metrics derived from email content. A significant logical flaw exists within the clean_found_uri function located in the parser.py file of versions prior to 3.0.2. This vulnerability stems from an overly restrictive validation mechanism that incorrectly processes URL strings containing HTML entities for specific punctuation characters such as colons, slashes, or periods. When these encoded URLs are encountered, the parsing logic fails to properly unescape them before validating their structure, leading to a false negative classification where valid and functional Uniform Resource Locators are erroneously rejected rather than accepted and processed correctly.
This technical deficiency results in the omission of legitimate host names from the extracted lists of URLs and domains generated by the parser. In operational security environments, email security gateways and Security Operations Center pipelines rely heavily on these parsed indicators to identify potential threats. By failing to extract valid encoded URLs, the system creates a blind spot that allows malicious actors to bypass inspection mechanisms. Attackers can leverage HTML entity encoding for standard URL delimiters to hide phishing links or malware distribution points within emails, effectively evading detection by systems that depend on accurate domain and URL extraction for threat intelligence correlation.
The impact of this vulnerability is substantial in the context of defensive security operations. When hidden URLs are not submitted to external threat intelligence feeds, reputation services, or sandboxing environments, organizations lose visibility into active campaigns targeting their users. This gap enables malicious links to remain undetected until they reach end-user mailboxes, increasing the risk of successful phishing attacks and subsequent compromise. The flaw represents a classic case where input validation logic is applied too rigidly, ignoring valid encoding schemes that are commonly used in both legitimate web development and adversarial evasion techniques.
From an industry standard perspective, this issue aligns with CWE-20 Improper Input Validation, as the application fails to correctly interpret encoded inputs that should be considered valid by design. Furthermore, it facilitates adversary tactics described in MITRE ATT&CK under T1566 Phishing, specifically where attackers use obfuscation techniques like HTML entity encoding to evade email security controls and deliver malicious payloads. The failure to process these indicators effectively undermines the integrity of automated threat detection pipelines that depend on accurate data extraction from email headers and bodies for proactive defense.
To mitigate this vulnerability, organizations must ensure they are running version 3.0.2 or later of the eml_parser module, which contains a fix for the clean_found_uri function to correctly handle HTML entities in URL validation logic. Security teams should also review their integration points with any third-party email parsing libraries to verify that updates have been applied consistently across all components of their mail processing infrastructure. Additionally, implementing defense-in-depth strategies such as heuristic analysis and behavioral monitoring can help detect malicious URLs even if they are not immediately extracted by the parser, providing a secondary layer of protection against evasion techniques that exploit parsing logic flaws.