CVE-2021-23406Network attack vector

Remote code execution via unsafe PAC code generation

Published Aug 24, 2021 · Updated Sep 17, 2024

Improper code generation in pac-resolver before 5.0.0 allows remote attackers to execute code via untrusted PAC files. The resolver passes PAC-derived JavaScript through the degenerator compiler and sandbox path without safely constraining generated code, allowing attacker-controlled script execution. Exploitation requires an application to process attacker-supplied PAC data; successful execution can compromise confidentiality, integrity, and availability.

CVSS severity9.8
Critical
EPSS probability2.86%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper code generation in pac-resolver before 5.0.0 allows remote attackers to execute code via untrusted PAC files. The resolver passes PAC-derived JavaScript through the degenerator compiler and sandbox path without safely constraining generated code, allowing attacker-controlled script execution. Exploitation requires an application to process attacker-supplied PAC data; successful execution can compromise confidentiality, integrity, and availability.

The record

CVE
CVE-2021-23406
Published
Aug 24, 2021
Updated
Sep 17, 2024
Vendor
TooTallNate
Product
pac-resolver
Classifications
T1059.007
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 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=unspecified <5.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

TooTallNate · pac-resolverversion=unspecified <5.0.0

Published CVSS scores

7.5[email protected]AV:N/AC:L/Au:N/C:P/I:P/A:P
9.8[email protected]CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/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 exploitUnconfirmed

Weakness, pattern, technique

T1059.007Command and Scripting Interpreter: JavaScript

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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