No exploitation reportedFix available

CVE-2021-33582

Q: Is CVE-2021-33582 actively exploited?

Active exploitation of CVE-2021-33582 has not been confirmed. Its EPSS score was 3.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

Q: What is the CVSS score for CVE-2021-33582?

CVE-2021-33582 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

No exploitation reported by the sources we read.

Published2021-09-01
Fixed in3.4.2 · 3.2.8 · 3.0.16
WeaknessCWE-407

Am I affected?

With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.

Description

Cyrus IMAP before 3.4.2 allows remote attackers to cause a denial of service (multiple-minute daemon hang) via input that is mishandled during hash-table interaction. Because there are many insertions into a single bucket, strcmp becomes slow. This is fixed in 3.4.2, 3.2.8, and 3.0.16.

Timeline

dates in UTC

2021-09-0106:15CVE publishedNVD

Observed activity

isMalicious corpus · updated 2026-10-23 18:48 UTC

Indicators tagged with this CVE, per day0 indicators over 7 days

Block these indicators

Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2021-33582?format=txt
CSV export: https://api.ismalicious.com/edl/cve/CVE-2021-33582?format=csv
TAXII collection of exploited CVEs
The EDL and CSV take an API key on the Pro plan.

Versions per branch

NVD

Cyrus imap

Branch	Affected	Fixed in	Source
3.4	≥ 3.4.0, < 3.4.2	3.4.2	NVD
3.2	≥ 3.2.0, < 3.2.8	3.2.8	NVD
3.0	< 3.0.16	3.0.16	NVD

Fedoraproject fedora

Branch	Affected	Fixed in	Source
34.x	= 34	no fix published	NVD
35.x	= 35	no fix published	NVD

Debian debian linux

Branch	Affected	Fixed in	Source
9.0	= 9.0	no fix published	NVD

as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.

Fix

Update Cyrus imap to 3.4.2 · 3.2.8 · 3.0.16

Advisories and patches

cyrus.topicbox.comPatch · Vendor Advisory
github.comPatch
www.cyrusimap.orgPatch · Release Notes · Vendor Advisory

Detection

Nuclei template: none so far
Exploit-DB: no entry
Proof-of-concept repositories: none listed

Sources

NVDCVSS 3.17.5read 2026-10-23
NVDCVSS 2.05read 2026-10-23
NVDweakness (CWE)CWE-407read 2026-10-23
FIRST EPSSEPSS score3.1 %2026-10-22

Technical details

CVSS v3 Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Published: 2021-09-01
Last Modified: 2026-06-17
NVD status: Modified

Frequently asked questions

What is CVE-2021-33582?

Is CVE-2021-33582 actively exploited?

Active exploitation of CVE-2021-33582 has not been confirmed. Its EPSS score was 3.1% on 2026-10-22, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2021-33582?

CVE-2021-33582 has a CVSS v3 base score of 7.5 (HIGH severity), with vector string CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

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