dbcve.org
FedoraOperating system · Fedoraproject

CVE-2021-32921

MEDIUM · 5.9 CVSS v3.1 Published 2021-05-13
Fix available
A fix is available. Upgrade to 0.11.9 or later.
See remediation →
68/100
Remediation priority · Elevated
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
An issue was discovered in Prosody before 0.11.9. It does not use a constant-time algorithm for comparing certain secret strings when running under Lua 5.2 or later. This can potentially be used in a timing attack to reveal the contents of secret strings to an attacker.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

Prosody before version 0.11.9 fails to use a constant-time comparison algorithm when validating secret strings under Lua 5.2 or later. This timing discrepancy allows attackers to potentially infer secret values by measuring how long string comparisons take, a classic timing side-channel attack.

MitigationUpgrade to Prosody 0.11.9 or later, which implements constant-time comparison for secret strings. If upgrade is not immediately possible, verify the Lua version in use and review any custom authentication modules for similar timing vulnerabilities.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
FedoraOperating system
Affected:= 32= 33= 34
Debian LinuxOperating system
Affected:= 9.0
ProsodyApplication
Affected:< 0.11.9

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check installed Prosody version
    Run `prosodyctl version` or check package manager: `rpm -q prosody` (Fedora/RHEL) or `dpkg -l prosody` (Debian)
    Affected if Version is below 0.11.9
  2. Check Lua interpreter version
    Run `lua -v` or `lua5.x -v` where x is 1-4, or check via Prosody: `prosodyctl about` shows Lua version under 'Lua' line
    Affected if Lua version is 5.2.0 or higher (the vulnerability only applies to Lua 5.2+)
  3. Verify Prosody is running with vulnerable Lua version
    Check which Lua binary Prosody uses: `ldd $(which prosody) | grep lua` or examine the Lua path Prosody was compiled against via `prosodyctl about` output
    Affected if Prosody is linked against Lua 5.2+ shared libraries while running a Prosody version below 0.11.9
  4. Inspect authentication configuration
    Review prosody.cfg.lua for `authentication` setting under the relevant VirtualHost or Component section; check for use of 'internal' or 'internal_plain' auth methods which handle secret validation
    Affected if Authentication method uses internal mechanisms that process user passwords or secrets (not applicable to anonymous or external auth)
  5. Check for custom authentication modules
    Inspect the plugins directory (typically /usr/lib/prosody/modules/ or /opt/prosody/modules/) for custom or third-party auth modules not part of standard Prosody distribution
    Affected if Custom authentication modules are loaded that may handle secret comparisons outside Prosody's core (could have independent timing vulnerabilities)

You are affected if running Prosody below version 0.11.9 with Lua 5.2 or later, and your deployment uses internal authentication methods that validate secret strings.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

From vendor data
Upgrade available Upgrade to 0.11.9 or later
Fixed in 0.11.9
Interim mitigation

Upgrade to Prosody 0.11.9 or later, which implements constant-time comparison for secret strings. If upgrade is not immediately possible, verify the Lua version in use and review any custom authentication modules for similar timing vulnerabilities.

Fix this in Fedora Scoped from the published advisory
  • Consultation2.0 h
  • Implementation1.0 h
  • Testing3.0 h
  • Review / QA2.0 h
8.0 hours of engineering $1,390
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2021-32921 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data