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CVE-2026-55620— eml_parser: DoS via deeply nested parens in Received headers

Quick assessment

Affected
GOVCERT-LU eml_parser
Exploitation
No confirmed in-the-wild exploitation; assess based on exposure
Recommended action
Check the vendor advisory and references for a fixed version. If immediate upgrade is impossible, restrict exposure and increase monitoring.

eml_parser 是一个用于解析 .eml 文件的 Python 模块，能够从电子邮件中提取各种信息，并生成计算得出的附加信息。在 3.0.2 版本之前， 中的 函数使用基于正则表达式的不动点循环来移除 头域中括号化的 CFWS（可折叠空白和注释）内容。该算法的运行时间随嵌套层数的平方增长，存在二次时间复杂度问题。一个仅包含 5,000 层嵌套括号单个 头域，每解析一条消息就会占用约 1.3 秒的 CPU 资源；而嵌套深度每增加一倍，运行时间大致增加四倍。 攻击者可以提交相对较小的 .eml 文件，导致处理过程

CVSS 7.5 · High

Possible ATT&CK Techniques 1 AI

T1496 · Resource Hijacking

Affected Version Matrix 1

VendorProduct Version RangeStatus
GOVCERT-LU eml_parser < 3.0.2 affected
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I. Basic Information for CVE-2026-55620

Vulnerability Information
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Vulnerability Title
eml_parser: DoS via deeply nested parens in Received headers
Source: CVE Program / CVE List V5
Vulnerability Description
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.
Source: CVE Program / CVE List V5
CVSS Information
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Source: CVE Program / CVE List V5
Vulnerability Type
不加限制或调节的资源分配
Source: CVE Program / CVE List V5

Affected Products

Vendor Product Affected Versions CPE Subscribe
GOVCERT-LU eml_parser < 3.0.2 -

II. Public POCs for CVE-2026-55620

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III. Intelligence Information for CVE-2026-55620

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Patches & Fixes for CVE-2026-55620 (3)

Vendor Advisories for CVE-2026-55620 (1)

Same Patch Batch · GOVCERT-LU · 2026-08-25 · 3 CVEs total

CVE-2026-55618 6.5 MEDIUM eml_parser: URL extraction bypass via HTML entities in URLs
CVE-2026-55619 5.3 MEDIUM eml_parser: Parser DoS via deeply nested parentheses in e-mail headers

IV. Related Vulnerabilities

Same product: eml_parser
Same vendor: GOVCERT-LU
Same weakness: CWE-770

V. Comments for CVE-2026-55620

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