CVE-2021-3711Network attack vector

Memory corruption via incorrect SM2 plaintext sizing

Published Aug 24, 2021 · Updated Sep 16, 2024

Heap buffer overflow in OpenSSL 1.1.1 through 1.1.1k allows remote attackers to corrupt memory via crafted SM2 ciphertext. The sm2_plaintext_size routine subtracts assumed fixed ASN.1 overhead from ciphertext length, so its first EVP_PKEY_decrypt call can report a buffer up to 62 bytes too small. Exploitation requires an application to decrypt attacker-controlled SM2 content with the two-call API pattern, allowing adjacent heap data changes or an application crash.

CVSS severity9.8
Critical
EPSS probability87.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Heap buffer overflow in OpenSSL 1.1.1 through 1.1.1k allows remote attackers to corrupt memory via crafted SM2 ciphertext. The sm2_plaintext_size routine subtracts assumed fixed ASN.1 overhead from ciphertext length, so its first EVP_PKEY_decrypt call can report a buffer up to 62 bytes too small. Exploitation requires an application to decrypt attacker-controlled SM2 content with the two-call API pattern, allowing adjacent heap data changes or an application crash.

The record

CVE
CVE-2021-3711
Published
Aug 24, 2021
Updated
Sep 16, 2024
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
CWE-120
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 16, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=Fixed in OpenSSL 1.1.1l (Affected 1.1.1-1.1.1k)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=Fixed in OpenSSL 1.1.1l (Affected 1.1.1-1.1.1k)

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-120Buffer Copy without Checking Size of Input ('Classic Buffer Overflow')

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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