Cyber Resilience

CVE-2026-42771

Memory Safety in Openssl 4.0.0

Memory Safety
Published
09 June 2026
Modified
17 June 2026
Patch / advisory
View advisory
CVSS Score v3.1 6.2
Click a component to see what it means
Raw vectorCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.0022 13th percentile
Risk Priority 46 floored blend · peak EPSS

Summary

CVE-2026-42771 is a medium-severity Out-of-bounds Read (CWE-125) vulnerability in Openssl Openssl. Its CVSS base score is 6.2 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Exploitation for Privilege Escalation (T1068); ranked at the 13th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.

The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SA-8 (Security and Privacy Engineering Principles) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-42771 is an out-of-bounds read in OpenSSL triggered when an application calls X509_VERIFY_PARAM_set1_email (or the related add variant) to validate a crafted email address, such as during S/MIME message processing. An internal helper function used an incorrect length when checking the local part of the address, allowing the documented 64-octet limit to be bypassed and producing a read past the end of the supplied buffer. The affected code lies outside the FIPS module boundary, so no FIPS-validated configurations are impacted.

An attacker who can supply a malicious From: header in an S/MIME-signed message can cause the validating application to crash, resulting in a denial of service. The CVSS vector (AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H) indicates the issue is locally reachable without authentication and produces a high availability impact while disclosing no data.

The OpenSSL project published advisory 20260609 and a corresponding fix in commit 6cd187689f8180c1f8a3acde21f88190c4a20de7 that corrects the length calculation used for local-part validation. Applications should update to a patched OpenSSL release and rebuild any components that perform S/MIME or X.509 email-address checks.

The current EPSS score remains at 0.0001 with no reported rise, and no in-the-wild exploitation has been observed.

EU & UK References

Vulnerability Data

Issue summary: When the X509_VERIFY_PARAM_set1_email is called by an application to validate a crafted e-mail address, such as during S/MIME message validation, an out of bounds read can happen. Impact summary: This out of bounds read will not directly exfiltrate…

more

the data read to the attacker so the most likely result is a crash and a Denial of Service. An internal helper function called from X509_VERIFY_PARAM_[set|add]_email() used a wrong length when validating the local part of an email address. This could cause the 64 octet limit on the local part of an email address to be not enforced, or cause an out of bound read and potentially a crash. The bug is reachable via S-MIME validation with a crafted From: address supplied in an email message that can potentially cause a crash. No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

CWE(s)
CWE-125

Related Threats

MITRE ATT&CK Enterprise Techniques

T1068 Exploitation for Privilege Escalation Privilege Escalation
Adversaries may exploit software vulnerabilities in an attempt to elevate privileges.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1203 Exploitation for Client Execution Execution
Adversaries may exploit software vulnerabilities in client applications to execute code.
attack.mitre.org →
T1210 Exploitation of Remote Services Lateral Movement
Adversaries may exploit remote services to gain unauthorized access to internal systems once inside of a network.
attack.mitre.org →
T1211 Exploitation for Stealth Stealth
Adversaries may exploit vulnerabilities to evade detection by hiding activity, suppressing logging, or operating within trusted or unmonitored components.
attack.mitre.org →
T1212 Exploitation for Credential Access Credential Access
Adversaries may exploit software vulnerabilities in an attempt to collect credentials.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-9076Same product: Openssl Openssl
CVE-2026-28386Same product: Openssl Openssl
CVE-2026-34180Same product: Openssl Openssl
CVE-2023-1255Same product: Openssl Openssl
CVE-2026-7383Same product: Openssl Openssl
CVE-2025-15467Same product: Openssl Openssl
CVE-2025-69419Same product: Openssl Openssl
CVE-2023-6129Same product: Openssl Openssl
CVE-2025-68160Same product: Openssl Openssl
CVE-2026-31789Same product: Openssl Openssl

Affected Assets

openssl
openssl
4.0.0

Mitigating Controls

Mitigating Controls (NIST 800-53 r5) AI

SA-11 Developer Testing and Evaluation good match

Developer testing and evaluation directly finds out-of-bounds read flaws through static analysis, fuzzing, and dynamic bounds checks.

SA-8 Security and Privacy Engineering Principles partial match

Secure engineering principles require bounds checking and memory-safe constructs that stop out-of-bounds reads from being introduced.

SC-39 Process Isolation partial match

Process isolation confines the effects of an out-of-bounds read to the compromised process.

SI-10 Information Input Validation partial match

Input validation rejects malformed indices or lengths that would otherwise cause reads outside buffer bounds.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 mostly match
prevents

Secure-development practices such as bounds checking and memory-safe languages directly prevent out-of-bounds reads.

ID.RA-01 partial match
prevents

Vulnerability scanning and recording can discover instances of out-of-bounds reads after code is deployed.

PR.PS-02 partial match
prevents

Routine patching replaces vulnerable code containing out-of-bounds read flaws.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing in development and acceptance includes fuzzing and static analysis that detect out-of-bounds read defects before release.

A.8.15 Logging partial match
finds

Logging can record evidence of an out-of-bounds read but does not prevent the weakness itself.

A.8.25 Secure development life cycle partial match
prevents

Secure development life cycle mandates input validation and bounds checking that directly prevent out-of-bounds reads.

A.8.26 Application security requirements partial match
prevents

Application security requirements include explicit bounds and memory-safety specifications that mitigate buffer over-reads.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure system architecture and engineering principles require memory-safe design patterns and runtime protections against out-of-bounds access.

A.8.28 Secure coding partial match
prevents

Secure coding standards explicitly forbid unsafe pointer arithmetic and mandate bounds-checked reads, eliminating CWE-125.

References