CVE-2026-55958Network attack vector

TLS client crash via unchecked transcript-buffer copy

Published Jun 25, 2026 · Updated Jun 25, 2026

Out-of-bounds write in wolfSSL 5.4.0 through 5.9.1 allows remote attackers to crash TSIP-enabled TLS 1.3 clients via oversized handshakes. The tsip_StoreMessage() capacity check sets MEMORY_E after MsgBag exceeds 8 KB but still calls XMEMCPY, writing beyond the fixed transcript buffer. Reachability requires a Renesas MCU build with WOLFSSL_RENESAS_TSIP_TLS and TSIP hardware, operating as a TLS 1.3 client.

CVSS severity8.3
High
EPSS probability0.44%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds write in wolfSSL 5.4.0 through 5.9.1 allows remote attackers to crash TSIP-enabled TLS 1.3 clients via oversized handshakes. The tsip_StoreMessage() capacity check sets MEMORY_E after MsgBag exceeds 8 KB but still calls XMEMCPY, writing beyond the fixed transcript buffer. Reachability requires a Renesas MCU build with WOLFSSL_RENESAS_TSIP_TLS and TSIP hardware, operating as a TLS 1.3 client.

The record

CVE
CVE-2026-55958
Published
Jun 25, 2026
Updated
Jun 25, 2026
Vendor
wolfSSL
Product
wolfSSL
Classifications
CWE-393, CWE-787, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Jun 25, 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=5.4.0 <=5.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

wolfSSL · wolfSSLversion=5.4.0 <=5.9.1

Published CVSS scores

8.3wolfSSL Inc.CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:H/SC:N/SI:N/SA:N
7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-393Return of Wrong Status Code
CWE-787Out-of-bounds Write
T1203Exploitation for Client Execution

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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