# CVE-2021-34337: Mailman Core timing attack on REST API password

Source: https://junglewise.ai/threats/cve-2021-34337-mailman-core-timing-attack-on-rest-api-password  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2023-04-15. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2021-34337 · Severity: low · CVSS 3.1 · Published 2023-04-15

Mailman Core is a widely-used mailing list management system. An attacker with access to the REST API could use timing attacks to guess the configured REST API password, then make unauthorized API calls to manage mailing lists and user subscriptions. By default the API only listens on localhost, limiting exposure, but administrators can optionally expose it on other network interfaces.

Technologies: [mailman (PyPI)](https://junglewise.ai/threats/technologies/mailman). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2021-34337 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2021-34337 being exploited in the wild.

**How severe is CVE-2021-34337?** Low severity, with a CVSS score of 3.1, published 15 April 2023.

**Which products and versions are affected?** Mailman Core before 3.3.5; mailman (PyPI) ECOSYSTEM:introduced=0,fixed=3.3.5, GIT:introduced=0,fixed=e4a39488c4510fcad8851217f10e7337a196bb51|ECOSYSTEM:introduced=0,fixed=3.3.5.

**Is there a fix for CVE-2021-34337?** Yes. mailman (PyPI): upgrade to 3.3.5 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2021-34337 attacked?** It is attacked with local access or over the network, in a hosted service.

**Am I affected by CVE-2021-34337?** Check whether you run Mailman Core or mailman (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- mailman (PyPI): upgrade to 3.3.5 or later

  ```sh
  pip install "mailman>=3.3.5"
  ```


## Technical details

The vulnerability is a timing attack (CWE-208) in Mailman Core's REST API password validation logic. An attacker with network access to the REST API endpoint can observe response time differences during password guessing attempts, allowing them to leak the password one character at a time. The REST API is bound to localhost by default, requiring an attacker to already have local system access or for the administrator to have configured the API to listen on other network interfaces. Once the password is compromised, an attacker can make arbitrary REST API calls to create/remove mailing lists, manage subscriptions, and access sensitive configuration. The vulnerability affects all versions before 3.3.5, which was patched to use constant-time password comparison.

## Affected products

- Mailman Mailman Core before 3.3.5

## Identifiers

- CVE-2021-34337
- GHSA-2jg5-xgvv-4wq7
- PYSEC-2023-22

## Timeline

- 2023-04-15: disclosed
- 2023-04-15: patched: version 3.3.5 released with fix

## References

- [https://github.com/pypa/advisory-database/tree/main/vulns/mailman/PYSEC-2023-22.yaml](https://github.com/pypa/advisory-database/tree/main/vulns/mailman/PYSEC-2023-22.yaml)

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- [PYSEC-2026-659 - mailman Cross-site scripting (XSS) vulnerability](https://junglewise.ai/threats/cve-2004-1177-mailman-cross-site-scripting-xss-vulnerability)
- [PYSEC-2026-658 - Mailman Sensitive Information Disclosure](https://junglewise.ai/threats/cve-2004-0412-mailman-sensitive-information-disclosure)
- [PYSEC-2026-657 - Mailman Cross-site scripting (XSS) vulnerability](https://junglewise.ai/threats/cve-2003-0038-mailman-cross-site-scripting-xss-vulnerability)
- [PYSEC-2026-660 - Cross Site Request Forgery in mailman](https://junglewise.ai/threats/cve-2021-44227-cross-site-request-forgery-in-mailman)
- [PYSEC-2026-661 - Moderate severity vulnerability that affects mailman](https://junglewise.ai/threats/cve-2018-13796-moderate-severity-vulnerability-that-affects-mailman)