CVE-2021-3712: OpenSSL ASN.1 string printing out-of-bounds read

Automated analysis

Generated by VULONE's analysis model from the NVD record, CISA KEV and EPSS data on 20 September 2026. Confidence: high.

high priorityCVSS 7.4 high severity with network reachability and high EPSS percentile, though exploitation requires an application that directly constructs ASN1_STRING structures.

What it is

OpenSSL functions that print ASN.1 data assume ASN1_STRING buffers are NUL terminated, but applications can construct valid ASN1_STRING structures without NUL termination via direct data/length assignment or ASN1_STRING_set0(). When such a string is printed or processed (including name constraints, X509_get1_email, X509_REQ_get1_email, X509_get1_ocsp), a read buffer overrun occurs. It matters because the overrun can crash the process or leak private memory such as keys or plaintext.

Impact

An attacker who can get an application to construct and then process a non-NUL-terminated ASN1_STRING can cause a denial of service via crash or read out-of-bounds memory, potentially disclosing private keys or sensitive plaintext.

Attack surface

Reached over the network (AV:N) with no privileges or user interaction required, but exploitation depends on the target application constructing ASN1_STRING structures directly rather than through OpenSSL parsing, which is why the vector rates complexity as high.

Exploitation

Not listed in CISA KEV and no ransomware usage documented; EPSS 30-day probability is about 0.50 (98.9th percentile), and references are advisories and patches rather than public exploit code.

What to do

• Upgrade OpenSSL to 1.1.1l or 1.0.2za (or later) on all affected hosts and embedded products.
• Apply vendor patches for downstream products (Debian, NetApp, McAfee, Oracle, Siemens, Tenable) that bundle OpenSSL.
• Audit application code for direct ASN1_STRING data/length assignment and ASN1_STRING_set0() use, and ensure NUL termination or avoid printing such strings.
• Track remaining exposure through SBOM or inventory of OpenSSL versions in appliances and third-party software.

Detection

• Search application and system logs for crashes or abnormal terminations in processes that print or parse ASN.1/X.509 data.
• Inventory OpenSSL versions across hosts and containers to find builds older than 1.1.1l or 1.0.2za.
• Monitor for unexpected memory disclosure patterns or anomalous certificate/ASN.1 processing errors in TLS and PKI services.

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