CVE-2021-39520Public exploitNetwork attack vector

Application crash via reconstruction null-pointer dereference

Published Sep 20, 2021 · Updated Aug 4, 2024

NULL pointer dereference in libjpeg through 2020021 allows remote attackers to crash image-processing applications with a crafted file. BlockBitmapRequester::PushReconstructedData() dereferences a null pointer at blockbitmaprequester.cpp line 1182 while reconstructing the malformed image. A user or calling application must process the file; the demonstrated consequence is termination of the decoding process.

CVSS severity6.5
Medium
EPSS probability0.87%
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 libjpeg through 2020021 allows remote attackers to crash image-processing applications with a crafted file. BlockBitmapRequester::PushReconstructedData() dereferences a null pointer at blockbitmaprequester.cpp line 1182 while reconstructing the malformed image. A user or calling application must process the file; the demonstrated consequence is termination of the decoding process.

The record

CVE
CVE-2021-39520
Published
Sep 20, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-476, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 20, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:N/A:P
6.5NIST NVDCVSS: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

CWE-476NULL Pointer Dereference
T1499.004Application or System Exploitation

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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