CVE-2021-32921Network attack vector

Secret-string disclosure via timing-dependent comparisons

Published May 13, 2021 · Updated Aug 3, 2024

Timing side channel in Prosody before 0.11.9 allows remote attackers to recover secret strings through repeated comparison attempts. Under Lua 5.2 or later, mod_auth_internal_plain and mod_muc use timing-dependent equality checks for passwords longer than 40 bytes instead of constant-time comparison. Both modules are disabled by default, and exploitation requires many failed guesses; exposure is limited to long user or password-protected-room secrets.

CVSS severity5.9
Medium
EPSS probability1.60%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing side channel in Prosody before 0.11.9 allows remote attackers to recover secret strings through repeated comparison attempts. Under Lua 5.2 or later, mod_auth_internal_plain and mod_muc use timing-dependent equality checks for passwords longer than 40 bytes instead of constant-time comparison. Both modules are disabled by default, and exploitation requires many failed guesses; exposure is limited to long user or password-protected-room secrets.

The record

CVE
CVE-2021-32921
Published
May 13, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-1254, CAPEC-26, T1110
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.7ProsodyCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:U
5.9NIST NVDCVSS: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

CWE-1254Incorrect Comparison Logic Granularity
CAPEC-26Leveraging Race Conditions
T1110Brute Force

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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