CVE-2021-28994Public exploitNetwork attack vector

Service crash via unbounded HTTP headers

Published Mar 31, 2021 · Updated Aug 3, 2024

Resource exhaustion in kopano-ical in Kopano Groupware Core and Zarafa allows remote attackers to crash the service with long HTTP headers. The HrReadHeaders routine accepts HTTP header lines without a length limit, continually allocates memory, and terminates on allocation failure. No authentication or user interaction is required; a network connection to the optional iCal/CalDAV service is enough to interrupt calendar access until the process restarts.

CVSS severity7.5
High
EPSS probability2.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Resource exhaustion in kopano-ical in Kopano Groupware Core and Zarafa allows remote attackers to crash the service with long HTTP headers. The HrReadHeaders routine accepts HTTP header lines without a length limit, continually allocates memory, and terminates on allocation failure. No authentication or user interaction is required; a network connection to the optional iCal/CalDAV service is enough to interrupt calendar access until the process restarts.

The record

CVE
CVE-2021-28994
Published
Mar 31, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-770, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 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

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

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 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 exploitPublished

Weakness, pattern, technique

CWE-770Allocation of Resources Without Limits or Throttling
T1499.003Application Exhaustion Flood

Public exploit references

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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