CVE-2021-4160Network attack vector

Private-key disclosure via missing MIPS carry propagation

Published Jan 28, 2022 · Updated Sep 16, 2024

Incorrect computation in BN_mod_exp in OpenSSL 1.0.2, 1.1.1 through 1.1.1l, and 3.0.0 allows remote attackers to recover private-key information. On MIPS32 and MIPS64, bn_sqr_comba4 and bn_sqr_comba8 fail to propagate a carry into the next result limb during modular exponentiation, producing incorrect cryptographic results. Useful disclosure requires repeated private-key use and substantial offline analysis; DH is considered just feasible, while RSA and DSA attacks are much harder.

CVSS severity5.9
Medium
EPSS probability3.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect computation in BN_mod_exp in OpenSSL 1.0.2, 1.1.1 through 1.1.1l, and 3.0.0 allows remote attackers to recover private-key information. On MIPS32 and MIPS64, bn_sqr_comba4 and bn_sqr_comba8 fail to propagate a carry into the next result limb during modular exponentiation, producing incorrect cryptographic results. Useful disclosure requires repeated private-key use and substantial offline analysis; DH is considered just feasible, while RSA and DSA attacks are much harder.

The record

CVE
CVE-2021-4160
Published
Jan 28, 2022
Updated
Sep 16, 2024
Vendor
OpenSSL Project
Product
OpenSSL
Classifications
T1552.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 28, 2022CVE 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 1.0.2zc-dev (Affected 1.0.2-1.0.2zb)
  2. Affected versionversion=Fixed in OpenSSL 1.1.1m (Affected 1.1.1-1.1.1l)
  3. Affected versionversion=Fixed in OpenSSL 3.0.1 (Affected 3.0.0)

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenSSL Project · OpenSSLversion=Fixed in OpenSSL 1.0.2zc-dev (Affected 1.0.2-1.0.2zb); version=Fixed in OpenSSL 1.1.1m (Affected 1.1.1-1.1.1l); version=Fixed in OpenSSL 3.0.1 (Affected 3.0.0)

Published CVSS scores

4.3NISTAV:N/AC:M/Au:N/C:P/I:N/A:N
5.9NISTCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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

T1552.004Unsecured Credentials: Private Keys

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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