What is CVE-2021-43838?

jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into ` ` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.

How severe is CVE-2021-43838?

CVE-2021-43838 has a CVSS 3.x base score of 5.3, rated medium 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 low.

Is CVE-2021-43838 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-43838?

CVE-2021-43838 affects Jsx-slack Project Jsx-slack. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-43838?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.

When was CVE-2021-43838 published?

CVE-2021-43838 was published on 2021-12-17 and last updated on 2026-06-17.

CVE-2021-43838

CVE-2021-43838 is a medium-severity vulnerability in Jsx-slack Project Jsx-slack with a CVSS 3.x base score of 5.3. 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: Medium (CVSS 3.x base score 5.3)
CVSS v2: 5.0
EPSS exploit prediction: 1% (69th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-1333
Affected product: Jsx-slack Project Jsx-slack
Published: 2021-12-17
Last modified: 2026-06-17

Description

jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `<blockquote>` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.

Frequently asked questions

What is CVE-2021-43838?: jsx-slack is a library for building JSON objects for Slack Block Kit surfaces from JSX. In versions prior to 4.5.1 users are vulnerable to a regular expression denial-of-service (ReDoS) attack. If attacker can put a lot of JSX elements into `<blockquote>` tag, an internal regular expression for escaping characters may consume an excessive amount of computing resources. jsx-slack v4.5.1 has patched to a regex for escaping blockquote characters. Users are advised to upgrade as soon as possible.
How severe is CVE-2021-43838?: CVE-2021-43838 has a CVSS 3.x base score of 5.3, rated medium 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 low.
Is CVE-2021-43838 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (69th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-43838?: CVE-2021-43838 affects Jsx-slack Project Jsx-slack. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-43838?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround.
When was CVE-2021-43838 published?: CVE-2021-43838 was published on 2021-12-17 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:jsx-slack_project:jsx-slack:*:*:*:*:*:node.js:*:*

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CVE-2021-43843 — Medium (CVSS 5.3): jsx-slack is a package for building JSON objects for Slack block kit surfaces from JSX. The maintainers found the patch…

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