CVE-2021-4241

Session-token prediction via weak randomness

Published Nov 15, 2022 · Updated Apr 15, 2025

Weak randomness in PHP Server Monitor before 3.6.0 allows attackers to predict values used in persistent authentication tokens. The newRememberMeCookie method hashes mt_rand() output for the rememberme cookie, so SHA-256 preserves the generator's predictability. Published assessments disagree on reachability, but both limit the reported consequence to confidentiality loss.

CVSS severity2.6
Low
EPSS probability0.82%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Weak randomness in PHP Server Monitor before 3.6.0 allows attackers to predict values used in persistent authentication tokens. The newRememberMeCookie method hashes mt_rand() output for the rememberme cookie, so SHA-256 preserves the generator's predictability. Published assessments disagree on reachability, but both limit the reported consequence to confidentiality loss.

The record

CVE
CVE-2021-4241
Published
Nov 15, 2022
Updated
Apr 15, 2025
Vendor
PHP Server Monitor
Product
PHP Server Monitor
Classifications
CWE-330, T1550.004
Attack vector
adjacent
Privileges
Unavailable

Timeline

How it unfolded

  1. Nov 15, 2022CVE publishedPublication date reported by the CVE source.
  2. Apr 15, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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  1. Affected versionversion=n/a

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesUnavailable in this record.

What is affected?

PHP Server Monitor · PHP Server Monitorversion=n/a

Published CVSS scores

5.3NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
2.6VulDB CNACVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:L/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
PrivilegesUnavailable
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-330Use of Insufficiently Random Values
T1550.004Use Alternate Authentication Material: Web Session Cookie

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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