CVE-2026-55619: Eml parser Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-m66c-fw79-6359
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CVSS 5.3
CWE-770 CWE-1124
Published
Advisory Summary

CVE-2026-55619 is a MODERATE (CVSS 5.3) denial of service vulnerability (CWE-770: Allocation of Resources Without Limits or Throttling) affecting Eml parser libraries in the PyPI ecosystem. The issue involves eml_parser has parser dos via deeply nested parentheses in e-mail headers. Remediation is available by upgrading affected packages to version 3.0.2.

CVE-2026-55619 at a Glance

CVE Identifier CVE-2026-55619
GHSA Identifier GHSA-m66c-fw79-6359
Severity MODERATE
CVSS v3.1 Base Score 5.3
CWE Classification CWE-770: Allocation of Resources Without Limits or Throttling
Affected Product Eml parser
Package Ecosystem PyPI
Published Date
Last Updated

Security Impact

CVSS: 5.3

The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L).

Attack Vector Network (AV:N)
Attack Complexity Low (AC:L)
Privileges Required None (PR:N)
User Interaction None (UI:N)
Scope Unchanged (S:U)
Confidentiality None (C:N)
Integrity None (I:N)
Availability Low (A:L)

How to Fix CVE-2026-55619

To remediate this vulnerability, upgrade all affected Eml parser dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

eml_parser fixed: 3.0.2 
pip install eml_parser>=3.0.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

pip show eml_parser

How to Check if You Are Affected

To determine whether your Python environment is affected by CVE-2026-55619, inspect your installed packages using pip:

pip show eml_parser

Analyze the terminal output to locate any version of Eml parser in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 3.0.2), your application is affected.

Note: The pip show eml_parser command checks currently installed packages in your active Python environment.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-770: Allocation of Resources Without Limits or Throttling, where the product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated. In Eml parser, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

### Summary `eml_parser` uses the `email.utils.getaddresses()` function from the CPython standard library to parse e-mail headers that contain e-mail addresses (such as `To`, `Cc`, `Bcc`, `From`, `Reply-To`, `Sender`, ...). When the input header contains a deeply nested CFWS (comment / folding white space) construct, the recursive descent parser in the standard library exhausts the call stack. The resulting `RecursionError` is not caught by `eml_parser`, so the exception propagates and aborts parsing of the whole message. ### Impact SOC pipelines use `eml_parser` to process untrusted e-mails. An attacker can easily create an eml file that will trigger the `RecursionError` during parsing. The impact is mitigated by the fact that there are various other situations in which `eml_parser` will raise an exception when attempting to parse a malformed or pathological eml file. In particular, very deeply nested multipart e-mails also result in a `RecursionError` being raised by the library voluntarily. Therefore, systems relying on `eml_parser` already need to detect and handle errors emanating from the library in an appropriate way. ### Workarounds The issue can be avoided by wrapping the call to `eml_parser.decode_email` or `eml_parser.decode_email_bytes` in a `try/except` construct. ### Patches Since version 3.0.2, `eml_parser` will catch the error in the standard library parser and fall back to a simpler parser based on a regular expression.

CVE-2026-55619 Affected Eml parser Versions

1 component(s)
Fixed Versions:
3.0.2
Product / Package Ecosystem Affected Versions Fixed Version
eml_parser
pypi/eml_parser
PyPI
< 3.0.2
3.0.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/GOVCERT-LU/eml_parser/security/advisories/GHSA-m66c-fw79-6359
Eml parser Source Repository REPOSITORY
https://github.com/GOVCERT-LU/eml_parser/pull/90
Security Fix Commit FIX COMMIT
https://github.com/GOVCERT-LU/eml_parser/commit/746a69f86443eb0b6a47f77db3cfe727c21f92b3
Eml parser Source Repository REPOSITORY
https://github.com/GOVCERT-LU/eml_parser
Eml parser Release RELEASE
https://github.com/GOVCERT-LU/eml_parser/releases/tag/v3.0.2

Frequently Asked Questions

What is CVE-2026-55619?
CVE-2026-55619 is a security vulnerability in Eml parser involving eml_parser has parser DoS via deeply nested parentheses in e-mail headers under CWE-770: Allocation of Resources Without Limits or Throttling.
Which Eml parser versions are affected?
Affected versions include releases prior to 3.0.2 across affected packages: eml_parser.
What version fixes CVE-2026-55619?
Upgrading to 3.0.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is eml_parser affected?
Yes, eml_parser is affected in releases prior to 3.0.2. Upgrade your dependency to 3.0.2 or later.
What is the CVSS score of CVE-2026-55619?
CVE-2026-55619 has a CVSS v3.1 base score of 5.3 (MODERATE) with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L.
What CWE is associated with CVE-2026-55619?
CVE-2026-55619 is classified under CWE-770: Allocation of Resources Without Limits or Throttling (The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.).
How can I check PyPI dependencies for CVE-2026-55619?
Run the dependency tree command: 'pip show eml_parser'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-m66c-fw79-6359",
  "modified" : "2026-08-25T18:25:47Z",
  "published" : "2026-08-25T18:25:47Z",
  "aliases" : [ "CVE-2026-55619" ],
  "summary" : "eml_parser has parser DoS via deeply nested parentheses in e-mail headers",
  "details" : "### Summary\n\n`eml_parser` uses the `email.utils.getaddresses()` function from the CPython standard library to parse e-mail headers that contain e-mail addresses (such as `To`, `Cc`, `Bcc`, `From`, `Reply-To`, `Sender`, ...). When the input header contains a deeply nested CFWS (comment / folding white space) construct, the recursive descent parser in the standard library exhausts the call stack. The resulting `RecursionError` is not caught by `eml_parser`, so the exception propagates and aborts parsing of the whole message.\n\n### Impact\n\nSOC pipelines use `eml_parser` to process untrusted e-mails. An attacker can easily create an eml file that will trigger the `RecursionError` during parsing.\n\nThe impact is mitigated by the fact that there are various other situations in which `eml_parser` will raise an exception when attempting to parse a malformed or pathological eml file. In particular, very deeply nested multipart e-mails also result in a `RecursionError` being raised by the library voluntarily. Therefore, systems relying on `eml_parser` already need to detect and handle errors emanating from the library in an appropriate way.\n\n### Workarounds\n\nThe issue can be avoided by wrapping the call to `eml_parser.decode_email` or `eml_parser.decode_email_bytes` in a `try/except` construct.\n\n### Patches\n\nSince version 3.0.2, `eml_parser` will catch the error in the standard library parser and fall back to a simpler parser based on a regular expression.",
  "severity" : [ {
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  "database_specific" : {
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    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-25T18:25:47Z",
    "nvd_published_at" : null
  }
}