Bug 2523719 (CVE-2026-55620)

Summary: CVE-2026-55620 eml_parser: eml_parser: Denial of Service via crafted email headers
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: high    
Version: unspecifiedKeywords: Security
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Hardware: All   
OS: Linux   
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A flaw was found in eml_parser, a Python module designed for parsing email files. A remote attacker can exploit a vulnerability in how the module processes `Received:` headers containing deeply nested parentheses. By submitting specially crafted email files, an attacker can cause excessive CPU usage, leading to significant processing delays, system slowdowns, and potential service outages. This can impact synchronous gateways, sandboxes, and real-time email triage systems.
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Bug Depends On: 2524366, 2524367    
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Description OSIDB Bzimport 2026-08-25 18:31:59 UTC 
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, eml_parser.routing.noparenthesis in eml_parser/routing.py removes parenthesized CFWS comments from Received: headers with a regex-based fix-point loop whose running time is quadratic in the nesting depth. A single Received: header with 5,000 nested parentheses causes approximately 1.3 seconds of CPU saturation per parsed message, and doubling the nesting depth approximately quadruples the running time. An attacker can submit relatively small EML files that consume multiple seconds of processing time, causing worker latency, queue backpressure, and possible service-level outages in synchronous gateways, sandboxes, and real-time triage pipelines. This issue is fixed in version 3.0.2.