CVE-2021-33196Network attack vector

Denial of service via unchecked ZIP file count

Published Aug 2, 2021 · Updated Aug 3, 2024

Denial of service in Go archive/zip before 1.15.13 and 1.16.0 through 1.16.4 allows attackers to crash applications with crafted ZIP files. Reader.init trusts the central-directory file count to preallocate the Reader.File slice before confirming that the archive contains that many entries. Impact requires a consuming application to pass an attacker-controlled archive to NewReader or OpenReader and is limited to a panic or fatal memory-exhaustion failure.

CVSS severity7.5
High
EPSS probability3.46%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Go archive/zip before 1.15.13 and 1.16.0 through 1.16.4 allows attackers to crash applications with crafted ZIP files. Reader.init trusts the central-directory file count to preallocate the Reader.File slice before confirming that the archive contains that many entries. Impact requires a consuming application to pass an attacker-controlled archive to NewReader or OpenReader and is limited to a panic or fatal memory-exhaustion failure.

The record

CVE
CVE-2021-33196
Published
Aug 2, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-20, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 2, 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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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
T1499Endpoint Denial of Service

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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