GHSA-hwj9-h5mp-3pm3 CVE-2021-23368

Regular Expression Denial of Service in postcss

Medium npm

Severity: 5.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 3.51%; Chance of exploitation in the next 30 days. Higher than 89.20% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-400 Uncontrolled Resource Consumption
Fix: 7.0.36; Upgrade postcss to this version or later

Description

The npm package postcss from 7.0.0 and before versions 7.0.36 and 8.2.10 is vulnerable to Regular Expression Denial of Service (ReDoS) during source map parsing.

Affected versions

npm

Package	Vulnerable	Fixed in
postcss	`>= 7.0.0, < 7.0.36`	`7.0.36`
postcss	`>= 8.0.0, < 8.2.10`	`8.2.10`

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.

postcss npm → `7.0.36`

npm

npm install postcss@7.0.36

yarn

yarn add postcss@7.0.36

pnpm

pnpm add postcss@7.0.36

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.

References

Advisories

nvd.nist.gov/vuln/detail/CVE-2021-23368

Timeline

Apr 12, 2021 Published
Jun 17, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-fxqj-rqcc-2cmp PostCSS: incomplete fix of GHSA-6g55-p6wh-862q — attacker-controlled sourceMappingURL reads arbitrary .map files when `from` is unset	Medium	Also affects postcss
GHSA-r28c-9q8g-f849 PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure	High	Also affects postcss
GHSA-6g55-p6wh-862q PostCSS: Arbitrary file read and information disclosure via attacker-controlled sourceMappingURL in CSS comments	Critical	Also affects postcss
GHSA-qx2v-qp2m-jg93 PostCSS has XSS via Unescaped </style> in its CSS Stringify Output	Medium	Also affects postcss
GHSA-7fh5-64p2-3v2j PostCSS line return parsing error	Medium	Also affects postcss
GHSA-566m-qj78-rww5 Regular Expression Denial of Service in postcss	High	Also affects postcss
GHSA-cggf-277g-3q54 pypdf has possible large memory usage when parsing page tree	High	Same weakness, CWE-400
GHSA-3g3m-2fjr-6pw4 Glob: AbortSignal cancellation bypass allows post-timeout filesystem traversal	Medium	Same weakness, CWE-400

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