How severe is CVE-2021-46743?

CVE-2021-46743 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.

Is CVE-2021-46743 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2021-46743?

CVE-2021-46743 affects Google Firebase Php-jwt. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2021-46743?

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

When was CVE-2021-46743 published?

CVE-2021-46743 was published on 2022-03-29 and last updated on 2026-06-17.

CVE-2021-46743

CVE-2021-46743 is a critical-severity vulnerability in Google Firebase Php-jwt with a CVSS 3.x base score of 9.1. 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-843.

Key facts

Severity: Critical (CVSS 3.x base score 9.1)
CVSS v2: 5.8
EPSS exploit prediction: 1% (54th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-843
Affected product: Google Firebase Php-jwt
Published: 2022-03-29
Last modified: 2026-06-17

Description

In Firebase PHP-JWT before 6.0.0, an algorithm-confusion issue (e.g., RS256 / HS256) exists via the kid (aka Key ID) header, when multiple types of keys are loaded in a key ring. This allows an attacker to forge tokens that validate under the incorrect key. NOTE: this provides a straightforward way to use the PHP-JWT library unsafely, but might not be considered a vulnerability in the library itself.

Frequently asked questions

What is CVE-2021-46743?: In Firebase PHP-JWT before 6.0.0, an algorithm-confusion issue (e.g., RS256 / HS256) exists via the kid (aka Key ID) header, when multiple types of keys are loaded in a key ring. This allows an attacker to forge tokens that validate under the incorrect key. NOTE: this provides a straightforward way to use the PHP-JWT library unsafely, but might not be considered a vulnerability in the library itself.
How severe is CVE-2021-46743?: CVE-2021-46743 has a CVSS 3.x base score of 9.1, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability none.
Is CVE-2021-46743 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 1% (54th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2021-46743?: CVE-2021-46743 affects Google Firebase Php-jwt. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2021-46743?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2021-46743 published?: CVE-2021-46743 was published on 2022-03-29 and last updated on 2026-06-17.

References

https://github.com/firebase/php-jwt/issues/351

Affected products (1)

cpe:2.3:a:google:firebase_php-jwt:*:*:*:*:*:*:*:*

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