CVE-2026-28490
Description
A flaw was found in Authlib, a Python library for building OAuth and OpenID Connect servers. This cryptographic padding oracle vulnerability, affecting the JSON Web Encryption (JWE) RSA1_5 key management algorithm, could allow a remote attacker to decrypt sensitive information. The vulnerability arises because Authlib registers RSA1_5 without requiring explicit opt-in and bypasses constant-time Bleichenbacher mitigations in the underlying cryptography library.
Statement
This MODERATE vulnerability in Authlib exposes a Bleichenbacher padding oracle in the JWE RSA1_5 implementation. Authlib enables RSA1_5 by default and breaks constant-time protections from the cryptography library. Remote attackers can exploit timing side-channels to decrypt encrypted tokens. Exploitation requires high complexity but no authentication. Impact is high confidentiality loss. Affects versions prior to 1.6.9.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 6.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | High | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | High | High | N/A |
| Integrity Impact | None | Low | N/A |
| Availability Impact | None | None | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
NVD: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:L/A:N
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
Confidentiality,Integrity
Technical Impact: Read Application Data; Modify Application Data
Accountability,Non-Repudiation
Technical Impact: Hide Activities
Frequently Asked Questions
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