CVE-2016-2108: OpenSSL ASN.1 negative zero buffer underflow allows remote code execution

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 18 September 2026. Confidence: high.

critical priorityCVSS 3.0 base score of 9.8 with network reachability, no authentication or interaction, and full confidentiality, integrity and availability impact, combined with a very high EPSS score.

What it is

OpenSSL's ASN.1 implementation mishandles an ANY field containing a negative zero value, causing a buffer underflow and memory corruption. The flaw affects OpenSSL before 1.0.1o and 1.0.2 before 1.0.2c and can be triggered by crafted serialized data. Because OpenSSL is widely embedded, the exposure spans servers, appliances and Android.

Impact

A remote attacker can execute arbitrary code in the context of the affected process or crash it, causing a denial of service. Successful code execution could give full control of the service handling the malformed ASN.1 data.

Attack surface

Reachable over the network with no authentication and no user interaction per the CVSS vector (AV:N/AC:L/PR:N/UI:N). Any service or application that parses attacker-supplied ASN.1 data with a vulnerable OpenSSL build is exposed.

Exploitation

Not listed in CISA KEV and no ransomware associations are documented. EPSS is high at 0.779 (99.5th percentile), indicating elevated predicted exploitation likelihood, but the record provides no confirmed in-the-wild exploitation evidence.

What to do

• Upgrade OpenSSL to 1.0.1o or later, or 1.0.2c or later, and apply vendor errata (Red Hat RHSA-2016-0722/0996/2056/2073, SUSE, Fedora, Slackware).
• Inventory embedded and statically linked OpenSSL copies (appliances, Android, third-party software) that package managers will not update.
• Where immediate patching is impossible, restrict or filter untrusted ASN.1 input at network boundaries and disable unnecessary services that parse such data.
• Rebuild or restart dependent services after upgrading the library so the patched code is loaded.
• Monitor vendor advisories for downstream products (Juniper, Apple) that bundle the affected OpenSSL versions.

Detection

• Search hosts and containers for OpenSSL versions below 1.0.1o or 1.0.2c using package inventory and file version checks.
• Monitor for crashes or abnormal process termination in services that parse ASN.1 (TLS, certificate handling, SNMP, LDAP).
• Watch for unexpected outbound connections or child processes spawned by services that handle untrusted ASN.1 data, which may indicate code execution.
• Alert on repeated malformed certificate or ASN.1 parse errors in application and TLS logs.

This assessment is produced automatically and is not human-reviewed. Verify against the vendor advisory before acting on it.