CVE-2026-4176Network attack vector

Service hang via nonterminating zlib shift loop

Published Mar 29, 2026 · Updated Mar 29, 2026

Vulnerable dependency handling in Perl allows attackers to hang applications through the bundled Compress::Raw::Zlib module. The vendored zlib x2nmodp routine right-shifts a negative length inside a loop whose termination condition is never reached. Reachability requires a Perl program to pass an attacker-influenced negative length to a CRC-combination operation, causing sustained CPU consumption without a demonstrated data-access impact.

CVSS severity9.8
Critical
EPSS probability0.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Vulnerable dependency handling in Perl allows attackers to hang applications through the bundled Compress::Raw::Zlib module. The vendored zlib x2nmodp routine right-shifts a negative length inside a loop whose termination condition is never reached. Reachability requires a Perl program to pass an attacker-influenced negative length to a CRC-combination operation, causing sustained CPU consumption without a demonstrated data-access impact.

The record

CVE
CVE-2026-4176
Published
Mar 29, 2026
Updated
Mar 29, 2026
Vendor
The Perl Foundation
Product
Perl
Classifications
CWE-1395, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 2026CVE publishedPublication date reported by the CVE source.
  2. Mar 29, 2026Record 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=5.41.0 <5.42.2-RC1
  2. Affected versionversion=5.43.0 <5.43.9
  3. Affected versionversion=5.9.4 <5.40.4-RC1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Perl Foundation · Perlversion=5.41.0 <5.42.2-RC1; version=5.43.0 <5.43.9; version=5.9.4 <5.40.4-RC1

Published CVSS scores

9.8CISA-ADPCVSS: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

CWE-1395Dependency on Vulnerable Third-Party Component
T1499Endpoint Denial of Service

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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