CVE-2026-5504Network attack vector

Plaintext recovery via incomplete CBC padding validation

Published Apr 9, 2026 · Updated Apr 9, 2026

Padding oracle in wolfSSL 5.9.0 and earlier allows remote attackers to recover PKCS7 CBC plaintext through repeated decryption queries. The PKCS7 CBC decryption path in wolfcrypt/src/pkcs7.c fails to validate interior padding bytes before accepting the decrypted block, exposing a validity distinction for modified ciphertext. Exploitation requires an application to accept attacker-modified PKCS7 ciphertext and reveal distinguishable decryption outcomes; plaintext disclosure is the only reported consequence.

CVSS severity6.3
Medium
EPSS probability0.11%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Padding oracle in wolfSSL 5.9.0 and earlier allows remote attackers to recover PKCS7 CBC plaintext through repeated decryption queries. The PKCS7 CBC decryption path in wolfcrypt/src/pkcs7.c fails to validate interior padding bytes before accepting the decrypted block, exposing a validity distinction for modified ciphertext. Exploitation requires an application to accept attacker-modified PKCS7 ciphertext and reveal distinguishable decryption outcomes; plaintext disclosure is the only reported consequence.

The record

CVE
CVE-2026-5504
Published
Apr 9, 2026
Updated
Apr 9, 2026
Vendor
wolfSSL
Product
wolfSSL
Classifications
CWE-354
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 9, 2026CVE publishedPublication date reported by the CVE source.
  2. Apr 9, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <=5.9.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

wolfSSL · wolfSSLversion=0 <=5.9.0

Published CVSS scores

6.3wolfSSL Inc.CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N
5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-354Improper Validation of Integrity Check Value

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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