How severe is CVE-2021-4305?

CVE-2021-4305 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-4305?

CVE-2021-4305 affects the following packages: robots-txt-guard (npm). Ecosystems affected: npm.

How do I fix CVE-2021-4305?

Update robots-txt-guard to 1.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4305 is resolved across your whole dependency graph.

How do I detect CVE-2021-4305 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for robots-txt-guard. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2021-4305 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-4305?

O3 pinpoints whether CVE-2021-4305 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-4305 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-4305 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-4305?

CVE-2021-4305 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 56th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2021-4305 published, and has it been updated?

CVE-2021-4305 was published on January 5, 2023 and was last updated on March 14, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-4305: robots-txt-guard (High 7.5)

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk56th percentile+0.45%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.

robots-txt-guardnpm

30Kdownloads / week

Description

A vulnerability was found in Woorank robots-txt-guard. It has been rated as problematic. Affected by this issue is the function makePathPattern of the file lib/patterns.js. The manipulation of the argument pattern leads to inefficient regular expression complexity. The exploit has been disclosed to the public and may be used. The name of the patch is c03827cd2f9933619c23894ce7c98401ea824020. It is recommended to apply a patch to fix this issue. The identifier of this vulnerability is VDB-217448.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`robots-txt-guard`	all versions	1.0.2

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for robots-txt-guard. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update robots-txt-guard to 1.0.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-4305 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-4305 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2021-4305. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

A vulnerability was found in Woorank robots-txt-guard. It has been rated as problematic. Affected by this issue is the function makePathPattern of the file lib/patterns.js. The manipulation of the argument pattern leads to inefficient regular expression complexity. The exploit has been disclosed to the public and may be used. The name of the patch is c03827cd2f9933619c23894ce7c98401ea824020. It is recommended to apply a patch to fix this issue. The identifier of this vulnerability is VDB-217448.

O3 Security · Impact-Aware SCA

Is CVE-2021-4305 in your dependencies?

O3 detects CVE-2021-4305 across npm dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works

CVE-2021-4305