How severe is CVE-2016-6309?

CVE-2016-6309 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2016-6309 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 70% (99th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2016-6309?

CVE-2016-6309 affects Openssl. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2016-6309?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2016-6309 published?

CVE-2016-6309 was published on 2016-09-26 and last updated on 2026-06-17.

CVE-2016-6309

CVE-2016-6309 is a critical-severity vulnerability in Openssl with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 70% places it in the 99th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-416.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 10.0
EPSS exploit prediction: 70% (99th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-416
Affected product: Openssl
Published: 2016-09-26
Last modified: 2026-06-17

Description

statem/statem.c in OpenSSL 1.1.0a does not consider memory-block movement after a realloc call, which allows remote attackers to cause a denial of service (use-after-free) or possibly execute arbitrary code via a crafted TLS session.

Frequently asked questions

What is CVE-2016-6309?: statem/statem.c in OpenSSL 1.1.0a does not consider memory-block movement after a realloc call, which allows remote attackers to cause a denial of service (use-after-free) or possibly execute arbitrary code via a crafted TLS session.
How severe is CVE-2016-6309?: CVE-2016-6309 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2016-6309 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 70% (99th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2016-6309?: CVE-2016-6309 affects Openssl. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2016-6309?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2016-6309 published?: CVE-2016-6309 was published on 2016-09-26 and last updated on 2026-06-17.

References

Affected products (1)

cpe:2.3:a:openssl:openssl:1.1.0a:*:*:*:*:*:*:*

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Other CWE-416 (Use After Free) vulnerabilities

CVE-2026-13782 — Critical (CVSS 10.0): Use after free in Browser in Google Chrome prior to 150.0.7871.47 allowed a remote attacker who had compromised the…
CVE-2026-4725 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Graphics: Canvas2D component. This vulnerability was fixed in Firefox 149…
CVE-2026-4688 — Critical (CVSS 10.0): Sandbox escape due to use-after-free in the Disability Access APIs component. This vulnerability was fixed in Firefox…
CVE-2025-24085 — Critical (CVSS 10.0): A use after free issue was addressed with improved memory management. This issue is fixed in iOS 18.3 and iPadOS 18.3,…
CVE-2024-43102 — Critical (CVSS 10.0): Concurrent removals of certain anonymous shared memory mappings by using the UMTX_SHM_DESTROY sub-request of…
CVE-2021-32495 — Critical (CVSS 10.0): Radare2 has a use-after-free vulnerability in pyc parser's get_none_object function. Attacker can read freed memory…

Browse all CWE-416 (Use After Free) vulnerabilities →