CVE-2021-3711 — SM2 Decryption Buffer Overflow

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

• Documented patch — www.oracle.com (NIST National Vulnerability Database)
• Documented patch — www.oracle.com (NIST National Vulnerability Database)
• Documented patch — www.oracle.com (NIST National Vulnerability Database)
• Rust Openssl-src: fixed in version 111.16.0 — github.com (GitHub Security Advisories)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

1. Identify exposed assets running the affected vendor/product/version combinations (Debian Debian Linux, Netapp Active Iq Unified Manager, Netapp Clustered Data Ontap…).
2. The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
3. Apply the fixed version or the patch documented under Remediation.
4. EPSS ahead of 100% of scored CVEs: prioritize it in the patch queue.
5. Search available logs for exploit probes matching the vulnerability class (memory corruption), errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-120 · Classic Buffer Overflow

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 87.82%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

• Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
• Correlate service crashes/restarts with inbound traffic; repeated crashes may indicate attempts.

Analysis and videos

CVE-2021-3711: OpenSSL SM2 Decryption Buffer Overflow
CVE-2021-3711 is a buffer overflow in the SM2 decryption code of OpenSSL. The buffer size calculated during the first EVP_PKEY_decrypt() call can be smaller than the size needed by the second call, which may let attacker-chosen data overflow the buffer by up to 62 bytes. The NVD record gives it a CVSS 3.1 score of 9.8 (critical), and the fix is in OpenSSL 1.1.1l. The CVE is not listed in CISA KEV and no confirmed exploitation appears in the sources consulted.

Timeline

What happened to this CVE, newest first.

• 2026
• Fix documented
  Oct 13, 2026 · GitHub Security Advisories
• Affected products added · rust/openssl-src
  Oct 13, 2026 · GitHub Security Advisories
• Affected products added · openssl/openssl
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• SSVC assessment updated
  Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
• Record published
  Oct 13, 2026
• Fix documented
  Oct 13, 2026 · NIST National Vulnerability Database
• CVSS changed · 9.8
  Oct 13, 2026 · NIST National Vulnerability Database
• Source status changed · → Modified
  Oct 13, 2026 · NIST National Vulnerability Database
• Record created in this database
  Oct 13, 2026 · NIST National Vulnerability Database
• 2021
• CVE published
  Aug 24, 2021 · openssl

Source activity

Repeated readings are counted rather than listed.

• 1× References added · Oct 13, 2026 – Oct 13, 2026
• 1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

26 on the record

• www.openssl.org/news/secadv/20210824.txt
  Vendor Advisory, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpuoct2021.html
  Patch, Third Party Advisory, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpujan2022.html
  Patch, Third Party Advisory, NIST National Vulnerability Database
• www.oracle.com/security-alerts/cpuapr2022.html
  Patch, Third Party Advisory, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20211022-0003
  GitHub Security Advisories
• lists.apache.org/thread.html/r18995de860f0e63635f3008fd2a6aca82394249476d21691e7c59c9e
  mailing-list, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20210827-0010/
  Third Party Advisory, NIST National Vulnerability Database
• git.openssl.org/gitweb/
  NIST National Vulnerability Database
• security.gentoo.org/glsa/202210-02
  Third Party Advisory, vendor-advisory, NIST National Vulnerability Database
• security.gentoo.org/glsa/202209-02
  Third Party Advisory, vendor-advisory, NIST National Vulnerability Database
• www.openwall.com/lists/oss-security/2021/08/26/2
  Mailing List, Third Party Advisory, mailing-list, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20211022-0003/
  Third Party Advisory, NIST National Vulnerability Database
• github.com/advisories/GHSA-5ww6-px42-wc85
  GitHub Security Advisories
• lists.apache.org/thread.html/rad5d9f83f0d11fb3f8bb148d179b8a9ad7c6a17f18d70e5805a713d1
  GitHub Security Advisories
• cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf
  Third Party Advisory, NIST National Vulnerability Database
• www.tenable.com/security/tns-2022-02
  Third Party Advisory, NIST National Vulnerability Database
• security.netapp.com/advisory/ntap-20240621-0006/
  NIST National Vulnerability Database
• lists.apache.org/thread.html/r18995de860f0e63635f3008fd2a6aca82394249476d21691e7c59c9e
  GitHub Security Advisories
• git.openssl.org/gitweb/
  GitHub Security Advisories
• security.netapp.com/advisory/ntap-20210827-0010
  GitHub Security Advisories
• www.tenable.com/security/tns-2021-16
  Third Party Advisory, NIST National Vulnerability Database
• lists.apache.org/thread.html/rad5d9f83f0d11fb3f8bb148d179b8a9ad7c6a17f18d70e5805a713d1
  mailing-list, NIST National Vulnerability Database
• rustsec.org/advisories/RUSTSEC-2021-0097.html
  GitHub Security Advisories
• security.netapp.com/advisory/ntap-20240621-0006
  GitHub Security Advisories
• www.debian.org/security/2021/dsa-4963
  Third Party Advisory, vendor-advisory, NIST National Vulnerability Database
• nvd.nist.gov/vuln/detail/CVE-2021-3711
  GitHub Security Advisories

Elsewhere on this site

Related CVEs (same products)

• High CVE-2026-84782 DTLS Retransmits Handshake Messages From a Stale Buffer Offset 16d
• High CVE-2026-84784 QUIC: Unbounded RETIRE_CONNECTION_ID Backlog 16d
• High CVE-2026-84783 Use-After-Free in X.509 Extension Cache Under Concurrent Use 16d
• Medium CVE-2026-75806 Unauthenticated and Undersized DTLS 1.2 AEAD Record Causes DoS 16d
• Low CVE-2026-77696 Timing Side-Channel in SM2 Signature Generation 16d
• Medium CVE-2026-75805 NULL Pointer Dereference in CMP Client Revocation Response Handling 16d

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

• No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
• No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
• No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2021-3711 is "SM2 Decryption Buffer Overflow", rated Critical. It affects Debian Linux (Debian); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.8 describes technical severity. EPSS 87.82% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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