CVE-2021-27836Public exploitNetwork attack vector

Process crash via unchecked worksheet pointer

Published Nov 3, 2021 · Updated Aug 3, 2024

NULL pointer dereference in the libxls 1.6.2 test programs allows context-dependent attackers to crash them via a crafted XLS file. When an XLS file has no BoundSheet8 record, xls_getWorkSheet returns NULL and test.c or test2.c passes it to xls_parseWorkSheet, which reads pWS->filepos without a NULL check. The flaw is reachable only in consumers that repeat this unchecked call pattern, and the demonstrated consequence is a process crash without reported data disclosure or modification.

CVSS severity6.5
Medium
EPSS probability1.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

NULL pointer dereference in the libxls 1.6.2 test programs allows context-dependent attackers to crash them via a crafted XLS file. When an XLS file has no BoundSheet8 record, xls_getWorkSheet returns NULL and test.c or test2.c passes it to xls_parseWorkSheet, which reads pWS->filepos without a NULL check. The flaw is reachable only in consumers that repeat this unchecked call pattern, and the demonstrated consequence is a process crash without reported data disclosure or modification.

The record

CVE
CVE-2021-27836
Published
Nov 3, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1499.004, T1204.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 3, 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

6.5UbuntuCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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

T1499.004Application or System Exploitation
T1204.002Malicious File

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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