CVE-2021-33582Network attack vector

Daemon hang via predictable hash-bucket collisions

Published Sep 1, 2021 · Updated Aug 3, 2024

Algorithmic complexity in Cyrus IMAP before 3.4.2 allows remote attackers to hang the daemon for minutes through crafted inputs. A predictable string hash lets attacker-controlled keys accumulate in one bucket, forcing every later insertion to compare against all existing entries with strcmp. No authentication or user interaction is required; the demonstrated consequence is CPU exhaustion and a multi-minute service hang.

CVSS severity7.5
High
EPSS probability3.09%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Algorithmic complexity in Cyrus IMAP before 3.4.2 allows remote attackers to hang the daemon for minutes through crafted inputs. A predictable string hash lets attacker-controlled keys accumulate in one bucket, forcing every later insertion to compare against all existing entries with strcmp. No authentication or user interaction is required; the demonstrated consequence is CPU exhaustion and a multi-minute service hang.

The record

CVE
CVE-2021-33582
Published
Sep 1, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-407, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 1, 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

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

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

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

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-407Inefficient Algorithmic Complexity
T1499.004Application or System Exploitation

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo