CVE-2023-48238Public exploitNetwork attack vector

JWT forgery via attacker-selected verification algorithm

Published Nov 17, 2023 · Updated Jun 8, 2026

Algorithm confusion in Joaquim Serafim json-web-token before 4.0.0 allows remote attackers to forge accepted JWT payloads. The decode path trusts the unverified header.alg value, treating an RSA public key as an HMAC secret when a token declares HS256. Exploitation requires an application configured for RS256 and access to its public key; successful tokens can supply arbitrary claims that the application accepts.

CVSS severity7.5
High
EPSS probability0.31%
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 Joaquim Serafim json-web-token before 4.0.0 allows remote attackers to forge accepted JWT payloads. The decode path trusts the unverified header.alg value, treating an RSA public key as an HMAC secret when a token declares HS256. Exploitation requires an application configured for RS256 and access to its public key; successful tokens can supply arbitrary claims that the application accepts.

The record

CVE
CVE-2023-48238
Published
Nov 17, 2023
Updated
Jun 8, 2026
Vendor
Joaquim Serafim
Product
json-web-token
Classifications
CWE-345
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 17, 2023CVE publishedPublication date reported by the CVE source.
  2. Jun 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 4.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Joaquim Serafim · json-web-tokenversion=< 4.0.0

Published CVSS scores

7.5GitHub CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/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-345Insufficient Verification of Data Authenticity

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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