How severe is CVE-2021-40900?

CVE-2021-40900 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.

Is CVE-2021-40900 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-40900?

CVE-2021-40900 affects Regexfn Project Regexfn. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-40900?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.

When was CVE-2021-40900 published?

CVE-2021-40900 was published on 2022-06-27 and last updated on 2026-06-17.

CVE-2021-40900

CVE-2021-40900 is a high-severity vulnerability in Regexfn Project Regexfn with a CVSS 3.x base score of 7.5. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-1333.

Key facts

Severity: High (CVSS 3.x base score 7.5)
CVSS v2: 5.0
EPSS exploit prediction: 1% (58th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1333
Affected product: Regexfn Project Regexfn
Published: 2022-06-27
Last modified: 2026-06-17

Description

A Regular Expression Denial of Service (ReDOS) vulnerability was discovered in regexfn v1.0.5 when validating crafted invalid emails.

Frequently asked questions

What is CVE-2021-40900?: A Regular Expression Denial of Service (ReDOS) vulnerability was discovered in regexfn v1.0.5 when validating crafted invalid emails.
How severe is CVE-2021-40900?: CVE-2021-40900 has a CVSS 3.x base score of 7.5, rated high severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is none, integrity none, and availability high.
Is CVE-2021-40900 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (58th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-40900?: CVE-2021-40900 affects Regexfn Project Regexfn. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-40900?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its high severity, prioritise patching exposed systems.
When was CVE-2021-40900 published?: CVE-2021-40900 was published on 2022-06-27 and last updated on 2026-06-17.

References

https://github.com/yetingli/SaveResults/blob/main/js/regexfn.js

Affected products (1)

cpe:2.3:a:regexfn_project:regexfn:1.0.5:*:*:*:*:node.js:*:*

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