CVE-2021-46743Public exploitNetwork attack vector

Token forgery via algorithm-unbound key selection

Published Mar 29, 2022 · Updated Aug 4, 2024

Algorithm confusion in Firebase PHP-JWT before 6.0.0 allows remote attackers to forge tokens when applications load mixed key types. The JWT::decode key-selection path trusts the attacker-controlled kid header to choose raw key material without binding the key to its permitted algorithm. The application must accept HMAC and RSA algorithms from a shared key ring; successful forgery grants the token's assigned access.

CVSS severity9.1
Critical
EPSS probability0.79%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Algorithm confusion in Firebase PHP-JWT before 6.0.0 allows remote attackers to forge tokens when applications load mixed key types. The JWT::decode key-selection path trusts the attacker-controlled kid header to choose raw key material without binding the key to its permitted algorithm. The application must accept HMAC and RSA algorithms from a shared key ring; successful forgery grants the token's assigned access.

The record

CVE
CVE-2021-46743
Published
Mar 29, 2022
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-347, CWE-843, T1550.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

9.1GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-347Improper Verification of Cryptographic Signature
CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
T1550.001Use Alternate Authentication Material: Application Access Token

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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