Padding Oracle Vulnerability in wolfSSL PKCS7 CBC Decryption

Publication date: 2026-04-09

Last updated on: 2026-04-29

Assigner: wolfSSL Inc.

Description

A padding oracle exists in wolfSSL's PKCS7 CBC decryption that could allow an attacker to recover plaintext through repeated decryption queries with modified ciphertext. In previous versions of wolfSSL the interior padding bytes are not validated.

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Meta Information

Published

2026-04-09

Last Modified

2026-04-29

Generated

2026-07-06

AI Q&A

2026-04-10

EPSS Evaluated

2026-07-05

NVD

CVE-2026-5504

EUVD

EUVD-2026-21235

Affected Vendors & Products

Vendor	Product	Version / Range
wolfssl	wolfssl	to 5.9.0 (inc)

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-354	The product does not validate or incorrectly validates the integrity check values or "checksums" of a message. This may prevent it from detecting if the data has been modified or corrupted in transmission.

Attack-Flow Graph

Executive Summary

This vulnerability is a padding oracle issue in wolfSSL's PKCS7 CBC decryption. It allows an attacker to recover plaintext data by making repeated decryption attempts with modified ciphertext. The problem arises because, in previous versions of wolfSSL, the interior padding bytes were not properly validated during decryption.

Impact Analysis

An attacker exploiting this vulnerability could recover sensitive plaintext data from encrypted communications or stored data by repeatedly querying the decryption function with altered ciphertext. This could lead to unauthorized disclosure of confidential information.

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