# CVE-2019-25102: simple-markdown regular expression denial of service

Source: https://junglewise.ai/threats/cve-2019-25102-simple-markdown-regular-expression-denial-of-service  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2023-02-12. Updated: 2026-09-25  
License: CC BY 4.0 with a link back

CVE-2019-25102 · Severity: low · CVSS 3.1 · Published 2023-02-12

simple-markdown is a JavaScript library for parsing Markdown content. A regular expression in the autolink parsing logic is vulnerable to denial of service through specially crafted input patterns, where a 5KB malicious document could take over 7 seconds to parse, consuming CPU resources and disrupting service availability.

Technologies: [simple-markdown (npm)](https://junglewise.ai/threats/technologies/simple-markdown). Vendors: [npm](https://junglewise.ai/threats/vendors/npm).

## Quick answers

**Is CVE-2019-25102 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2019-25102 being exploited in the wild.

**How severe is CVE-2019-25102?** Low severity, with a CVSS score of 3.1, published 12 February 2023.

**Which products and versions are affected?** simple-markdown (npm) SEMVER:introduced=0,fixed=0.6.1.

**Is there a fix for CVE-2019-25102?** Yes. simple-markdown (npm): upgrade to 0.6.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2019-25102 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2019-25102?** Check whether you run simple-markdown (npm) 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

- simple-markdown (npm): upgrade to 0.6.1 or later

  ```sh
  npm install simple-markdown@0.6.1
  ```


## Technical details

The vulnerability is a Regular Expression Denial of Service (ReDoS) in the autolink pattern matching of simple-markdown.js, caused by inefficient regex complexity (O(n³) in affected versions). The vulnerable pattern fails to properly handle malformed input like "<<<<<<<<<<:/:/:/:/:/:/:/:/:/:/" which triggers catastrophic backtracking. The attack is remotely exploitable without authentication or user interaction—any attacker who can provide markdown input to an application using simple-markdown can trigger excessive CPU consumption. The vulnerability was fixed in version 0.6.1 (commit 015a719bf5cdc561feea05500ecb3274ef609cd2) by refactoring the autolink regex to reduce complexity from O(n³) to O(n²).

## Affected products

- simple-markdown simple-markdown 0.6.0 and prior; fixed in 0.6.1

## Identifiers

- CVE-2019-25102
- GHSA-j533-2g8v-pmpg

## Timeline

- 2019-09: disclosed: Public GitHub PR disclosure
- 2019-09-26: patched: Fix merged in commit 015a719bf5cdc561feea05500ecb3274ef609cd2
- 2023-02-12: advisory: GitHub advisory GHSA-j533-2g8v-pmpg published

## References

- [https://github.com/ariabuckles/simple-markdown/pull/73](https://github.com/ariabuckles/simple-markdown/pull/73)

## Related threats

- [simple-markdown regular expression denial of service](https://junglewise.ai/threats/cve-2019-25103-simple-markdown-regular-expression-denial-of-service)
- [simple-markdown regular expression denial of service](https://junglewise.ai/threats/simple-markdown-regular-expression-denial-of-service-a4876976)
- [simple-markdown cross-site scripting in link handling](https://junglewise.ai/threats/cve-2019-9844-simple-markdown-cross-site-scripting-in-link-handling)