CVE-2021-4286Network attack vector

Password-secret disclosure via variable-time modular exponentiation

Published Dec 27, 2022 · Updated Apr 11, 2025

Timing side channel in cocagne pysrp 1.0.16 and earlier allows remote attackers to infer password-derived secrets during SRP exchanges. In srp/_ctsrp.py, calculate_x leaves the password-derived BIGNUM without BN_FLG_CONSTTIME, so OpenSSL modular exponentiation can vary with secret values. Exploitation requires an observer able to submit and time repeated SRP authentication operations; disclosed impact is limited to confidentiality.

CVSS severity7.5

High

EPSS probability0.70%

Next 30 days · Sep 16, 2026

Known exploitationUnconfirmed

Based on sourced intelligence

Hinoki checkNot available

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Summary

What happened

The record

CVE: CVE-2021-4286
Published: Dec 27, 2022
Updated: Apr 11, 2025

Vendor: cocagne
Product: pysrp
Classifications: CWE-203

Attack vector: network
Privileges: unauthenticated

Timeline

How it unfolded

Dec 27, 2022CVE publishedPublication date reported by the CVE source.
Apr 11, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

Affected versionversion=1.0.0
Affected versionversion=1.0.1
Affected versionversion=1.0.10
Affected versionversion=1.0.11
Affected versionversion=1.0.12
Affected versionversion=1.0.13
Affected versionversion=1.0.14
Affected versionversion=1.0.15
Affected versionversion=1.0.16
Affected versionversion=1.0.2
Affected versionversion=1.0.3
Affected versionversion=1.0.4
Affected versionversion=1.0.5
Affected versionversion=1.0.6
Affected versionversion=1.0.7
Affected versionversion=1.0.8
Affected versionversion=1.0.9

What conditions does exploitation require?

Attack vectornetwork

Required privilegesunauthenticated

What is affected?

cocagne · pysrpversion=1.0.0; version=1.0.1; version=1.0.10; version=1.0.11; version=1.0.12; version=1.0.13; version=1.0.14; version=1.0.15; version=1.0.16; version=1.0.2; version=1.0.3; version=1.0.4; version=1.0.5; version=1.0.6; version=1.0.7; version=1.0.8; version=1.0.9

Published CVSS scores

2.6VulDBCVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N

7.5NIST NVDCVSS:3.1/AV:N/AC:L/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 9, 2026Sep 15, 2026

Latest reporting daySep 15, 2026

Latest daily unique IPsUnavailable

Prior 30-day averageUnavailable

SourceShadowserver honeypots (KEV)

Vectornetwork

Privilegesunauthenticated

Known exploitationUnconfirmed

Public exploitUnconfirmed

Weakness, pattern, technique

CWE-203Observable Discrepancy

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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