CVE-2021-1252Network attack vector

Scanning process hang via XLM parser loop

Published Apr 8, 2021 · Updated Nov 8, 2024

Infinite loop in Cisco ClamAV 0.103.0 and 0.103.1 allows remote attackers to hang the scanning process with a crafted Excel file. The Excel XLM macro parser improperly handles an error and continues processing crafted input in a loop with no reachable exit. Exploitation requires only that an affected scanner process the supplied file; the reported consequence is limited to interruption of the scanning process.

CVSS severity7.5
High
EPSS probability2.52%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite loop in Cisco ClamAV 0.103.0 and 0.103.1 allows remote attackers to hang the scanning process with a crafted Excel file. The Excel XLM macro parser improperly handles an error and continues processing crafted input in a loop with no reachable exit. Exploitation requires only that an affected scanner process the supplied file; the reported consequence is limited to interruption of the scanning process.

The record

CVE
CVE-2021-1252
Published
Apr 8, 2021
Updated
Nov 8, 2024
Vendor
ClamAV
Product
ClamAV
Classifications
CWE-20, CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 8, 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?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0.103.0
  2. Affected versionversion=0.103.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

ClamAV · ClamAVversion=0.103.0; version=0.103.1

Published CVSS scores

7.5Cisco Systems, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.8NIST NVDAV:N/AC:L/Au:N/C:N/I:N/A:C

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-20Improper Input Validation
CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')
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

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Your stack

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