CVE-2017-11424: In PyJWT 1.5.0 and below the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys

Description

In PyJWT 1.5.0 and below the `invalid_strings` check in `HMACAlgorithm.prepare_key` does not account for all PEM encoded public keys. Specifically, the PKCS1 PEM encoded format would be allowed because it is prefaced with the string `-----BEGIN RSA PUBLIC KEY-----` which is not accounted for. This enables symmetric/asymmetric key confusion attacks against users using the PKCS1 PEM encoded public keys, which would allow an attacker to craft JWTs from scratch.

CVSS vector

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Attack vector

Network

Complexity

Low

Privileges

None

User interaction

None

Confidentiality

None

Integrity

High

Availability

None

Scope

Unchanged

Exploitation

Is it being used?

Exploit prediction (EPSS)1.8% · higher than 78% of CVEs

Exploited in the wildNo evidence yet

CISA KEVNot listed

Ransomware campaign useNot known

Affected products

Which versions

DL

Debian Linux · Debian

8.0; 9.0 · source: NVD

PY

Pyjwt · Pyjwt Project

through 1.5.0 · source: NVD