CVE-2021-3711 | SM2 Decryption Buffer Overflow

In order to decrypt SM2 encrypted data an application is expected to call the API function EVP_PKEY_decrypt(). Typically an application will call this function twice. The first time, on entry, the "out" parameter can be NULL and, on exit, the "outlen" parameter is populated with the buffer size required to hold the decrypted plaintext. The application can then allocate a sufficiently sized buffer and call EVP_PKEY_decrypt() again, but this time passing a non-NULL value for the "out" parameter. A bug in the implementation of the SM2 decryption code means that the calculation of the buffer size required to hold the plaintext returned by the first call to EVP_PKEY_decrypt() can be smaller than the actual size required by the second call. This can lead to a buffer overflow when EVP_PKEY_decrypt() is called by the application a second time with a buffer that is too small. A malicious attacker who is able present SM2 content for decryption to an application could cause attacker chosen data to overflow the buffer by up to a maximum of 62 bytes altering the contents of other data held after the buffer, possibly changing application behaviour or causing the application to crash. The location of the buffer is application dependent but is typically heap allocated. Fixed in OpenSSL 1.1.1l (Affected 1.1.1-1.1.1k).

Published: 2021-08-24 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]

Conclusion & alert: CVE-2021-3711 is rated High Risk (79.1/100): CVSS Critical severity, with high exploitation likelihood (EPSS 87.82%, 100th percentile). Core evidence: EPSS ranks this CVE among the most likely to be exploited in the near term. EPSS rose +85.27% over the last day, indicating growing attacker interest. Mandatory action: High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2021-3711

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 2.54% 87.82% +85.27%
2 2026-05-24 2.37% 2.54% +0.17%
3 2026-04-21 2.37%

Full EPSS history (89 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3711

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
9.8 3.1 CRITICAL
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:H)
Serious risk that confidential data gets exposed in a big way.
Integrity (I:H)
They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
3.9 5.9 [email protected]
7.5 2.0 HIGH
AV:N/AC:L/Au:N/C:P/I:P/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:P)
Partial confidentiality impact.
Integrity impact (I:P)
Partial integrity impact.
Availability impact (A:P)
Partial availability impact.
10.0 6.4 [email protected]

Weakness enumeration for CVE-2021-3711

GitHub Security Advisory for CVE-2021-3711

GHSA-5ww6-px42-wc85 · Severity: critical · Ecosystem: rust — SM2 Decryption Buffer Overflow

OS Trackers for CVE-2021-3711

vendor priority summary link
alpine critical CVE-2021-3711: 3 source package rows (openssl, openssl1.1-compat, openssl3); 54 state rows across 12 repos (3.11-main, 3.12-main, 3.17-community, 3.17-main, 3.18-community, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-community, edge-main); fixed 14, open 40. https://security.alpinelinux.org/vuln/CVE-2021-3711
debian not yet assigned CVE-2021-3711 not yet assigned priority: Debian including 1 source packages (openssl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-3711
gentoo normal CVE-2021-3711: 2 GLSA(s) (202209-02, 202210-02), 2 atom(s) (app-backup/tsm, dev-libs/openssl); latest impact normal. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-3711
redhat high https://access.redhat.com/security/cve/CVE-2021-3711
suse critical CVE-2021-3711 severity critical: SUSE including 469 source package names (0.21.0.3.2.10:libopenssl1_1-1.1.1d-11.27.1, 0.21.0.3.2.10:libopenssl1_1-hmac-1.1.1d-11.27.1, …), 931 product×package rows across 191 product lines (Container bci/bci-init, Container bci/dotnet-aspnet, … (191 product lines)): Fixed 457, Known Not Affected 326, Known Affected 148. https://www.suse.com/security/cve/CVE-2021-3711/
ubuntu high CVE-2021-3711 high priority: Ubuntu including 4 source packages (edk2, nodejs, openssl, openssl1.0), 60 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 30, DNE 14, released 13, needs-triage 3. https://ubuntu.com/security/CVE-2021-3711

Affected software / configurations for CVE-2021-3711

Vendor Product Version Raw CPE
openssl openssl >= 1.1.1, < 1.1.1l cpe:2.3:a:openssl:openssl:*:*:*:*:*:*:*:*
debian debian_linux 10.0 cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
netapp active_iq_unified_manager cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:vmware_vsphere:*:*
netapp active_iq_unified_manager cpe:2.3:a:netapp:active_iq_unified_manager:-:*:*:*:*:windows:*:*
netapp clustered_data_ontap cpe:2.3:a:netapp:clustered_data_ontap:-:*:*:*:*:*:*:*
netapp clustered_data_ontap_antivirus_connector cpe:2.3:a:netapp:clustered_data_ontap_antivirus_connector:-:*:*:*:*:*:*:*
netapp e-series_santricity_os_controller >= 11.0, <= 11.50.2 cpe:2.3:a:netapp:e-series_santricity_os_controller:*:*:*:*:*:*:*:*
netapp hci_management_node cpe:2.3:a:netapp:hci_management_node:-:*:*:*:*:*:*:*
netapp manageability_software_development_kit cpe:2.3:a:netapp:manageability_software_development_kit:-:*:*:*:*:*:*:*
netapp oncommand_insight cpe:2.3:a:netapp:oncommand_insight:-:*:*:*:*:*:*:*
netapp oncommand_workflow_automation cpe:2.3:a:netapp:oncommand_workflow_automation:-:*:*:*:*:*:*:*
netapp santricity_smi-s_provider cpe:2.3:a:netapp:santricity_smi-s_provider:-:*:*:*:*:*:*:*
netapp snapcenter cpe:2.3:a:netapp:snapcenter:-:*:*:*:*:*:*:*
netapp solidfire cpe:2.3:a:netapp:solidfire:-:*:*:*:*:*:*:*
netapp storage_encryption cpe:2.3:a:netapp:storage_encryption:-:*:*:*:*:*:*:*
oracle communications_cloud_native_core_security_edge_protection_proxy 1.7.0 cpe:2.3:a:oracle:communications_cloud_native_core_security_edge_protection_proxy:1.7.0:*:*:*:*:*:*:*
oracle communications_cloud_native_core_unified_data_repository 1.15.0 cpe:2.3:a:oracle:communications_cloud_native_core_unified_data_repository:1.15.0:*:*:*:*:*:*:*
oracle communications_session_border_controller 8.4 cpe:2.3:a:oracle:communications_session_border_controller:8.4:*:*:*:*:*:*:*
oracle communications_session_border_controller 9.0 cpe:2.3:a:oracle:communications_session_border_controller:9.0:*:*:*:*:*:*:*
oracle communications_unified_session_manager 8.2.5 cpe:2.3:a:oracle:communications_unified_session_manager:8.2.5:*:*:*:*:*:*:*
oracle communications_unified_session_manager 8.4.5 cpe:2.3:a:oracle:communications_unified_session_manager:8.4.5:*:*:*:*:*:*:*
oracle enterprise_communications_broker 3.2.0 cpe:2.3:a:oracle:enterprise_communications_broker:3.2.0:*:*:*:*:*:*:*
oracle enterprise_communications_broker 3.3.0 cpe:2.3:a:oracle:enterprise_communications_broker:3.3.0:*:*:*:*:*:*:*
oracle enterprise_session_border_controller 8.4 cpe:2.3:a:oracle:enterprise_session_border_controller:8.4:*:*:*:*:*:*:*
oracle enterprise_session_border_controller 9.0 cpe:2.3:a:oracle:enterprise_session_border_controller:9.0:*:*:*:*:*:*:*
oracle essbase < 11.1.2.4.47 cpe:2.3:a:oracle:essbase:*:*:*:*:*:*:*:*
oracle essbase >= 21.1, < 21.3 cpe:2.3:a:oracle:essbase:*:*:*:*:*:*:*:*
oracle health_sciences_inform_publisher 6.2.1.1 cpe:2.3:a:oracle:health_sciences_inform_publisher:6.2.1.1:*:*:*:*:*:*:*
oracle health_sciences_inform_publisher 6.3.1.1 cpe:2.3:a:oracle:health_sciences_inform_publisher:6.3.1.1:*:*:*:*:*:*:*
oracle jd_edwards_enterpriseone_tools < 9.2.6.3 cpe:2.3:a:oracle:jd_edwards_enterpriseone_tools:*:*:*:*:*:*:*:*
oracle jd_edwards_world_security a9.4 cpe:2.3:a:oracle:jd_edwards_world_security:a9.4:*:*:*:*:*:*:*
oracle mysql_connectors <= 8.0.27 cpe:2.3:a:oracle:mysql_connectors:*:*:*:*:*:*:*:*
oracle mysql_enterprise_monitor <= 8.0.25 cpe:2.3:a:oracle:mysql_enterprise_monitor:*:*:*:*:*:*:*:*
oracle mysql_server >= 5.7.0, <= 5.7.35 cpe:2.3:a:oracle:mysql_server:*:*:*:*:*:*:*:*
oracle mysql_server >= 8.0.0, <= 8.0.26 cpe:2.3:a:oracle:mysql_server:*:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.57 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.57:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.58 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.58:*:*:*:*:*:*:*
oracle peoplesoft_enterprise_peopletools 8.59 cpe:2.3:a:oracle:peoplesoft_enterprise_peopletools:8.59:*:*:*:*:*:*:*
oracle zfs_storage_appliance_kit 8.8 cpe:2.3:a:oracle:zfs_storage_appliance_kit:8.8:*:*:*:*:*:*:*
tenable nessus_network_monitor <= 5.13.1 cpe:2.3:a:tenable:nessus_network_monitor:*:*:*:*:*:*:*:*
tenable tenable.sc >= 5.16.0, <= 5.19.1 cpe:2.3:a:tenable:tenable.sc:*:*:*:*:*:*:*:*

References for CVE-2021-3711

URL Tags
http://www.openwall.com/lists/oss-security/2021/08/26/2 Mailing List Third Party Advisory
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf Third Party Advisory
https://git.openssl.org/gitweb/?p=openssl.git%3Ba=commitdiff%3Bh=59f5e75f3bced8fc0e130d72a3f582cf7b480b46
https://lists.apache.org/thread.html/r18995de860f0e63635f3008fd2a6aca82394249476d21691e7c59c9e%40%3Cdev.tomcat.apache.org%3E
https://lists.apache.org/thread.html/rad5d9f83f0d11fb3f8bb148d179b8a9ad7c6a17f18d70e5805a713d1%40%3Cdev.tomcat.apache.org%3E
https://security.gentoo.org/glsa/202209-02 Third Party Advisory
https://security.gentoo.org/glsa/202210-02 Third Party Advisory
https://security.netapp.com/advisory/ntap-20210827-0010/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20211022-0003/ Third Party Advisory
https://security.netapp.com/advisory/ntap-20240621-0006/
https://www.debian.org/security/2021/dsa-4963 Third Party Advisory
https://www.openssl.org/news/secadv/20210824.txt Vendor Advisory
https://www.oracle.com/security-alerts/cpuapr2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpujan2022.html Patch Third Party Advisory
https://www.oracle.com/security-alerts/cpuoct2021.html Patch Third Party Advisory
https://www.tenable.com/security/tns-2021-16 Third Party Advisory
https://www.tenable.com/security/tns-2022-02 Third Party Advisory
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