CVE-2021-3711

What it is

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).

At a glance

Exploitability

Can be exploited over the network without logging in. High risk of data exposure, data tampering, service disruption.

Exploit odds

87.8% chance of exploitation in the next 30 days (EPSS). Higher than most.

Fix

A patch, advisory or fixed version is referenced. Upgrade or apply it.

Timeline

1. 2021-08-16 00:00 UTC ReservedThe CVE id was reserved by its CNA
2. 2021-08-24 15:15 UTC PublishedDisclosed publicly on CVE.org and NVD
3. 2026-10-08 21:17 UTC Last updatedMost recent change to the record

Why it ranks here

• Exploited in the wild: no, CISA does not list it.
• Exploit odds: 87.8% in the next 30 days (EPSS).
• Severity: 9.8 CRITICAL (CVSS).
• Fix: a patch or advisory is linked.
• It meets the bar for Drop everything: critical, and exploited or very likely to be.

Details

Published

2021-08-24 15:15 UTC

Last modified

2026-10-08 21:17 UTC

Exploit probability

87.8% · EPSS, next 30 days

Weakness

CWE-120 · Classic buffer overflow

Record status

Modified

Affected

• OpenSSL < 1.1.1l
• Debian Linux 10.0
• Debian Linux 11.0
• Netapp Active Iq Unified Manager
• Netapp Clustered Data Ontap
• Netapp Clustered Data Ontap Antivirus Connector
• Netapp e-series Santricity Os Controller ≤ 11.50.2
• Netapp Hci Management Node

Attack profile CVSS 3.1 · 9.8

Attack vector

Network

Complexity

Low

Privileges needed

None

User interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Is it in your code?

Hand this to your coding agent. It searches your project for the affected products and checks versions. Nothing leaves your machine.

Read https://cve-list.com/agent/cve/CVE-2021-3711.md and follow it. Check whether this project is affected by CVE-2021-3711. Read only. Don't change anything and don't upload my code. Tell me yes, no or not sure, with the file as proof.

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