CVE-2021-4185Public exploitNetwork attack vector

Analysis hang via signed AMF length underflow

Published Dec 30, 2021 · Updated Nov 3, 2025

Infinite-loop denial of service in Wireshark 3.4.0 through 3.4.10 and 3.6.0 allows remote attackers to hang analysis via crafted RTMP data. In rtmpt_get_amf_length, an attacker-controlled 32-bit AMF string or XML length is stored in a signed integer; an underflow can leave rv at zero so the loop condition never clears. The hang consumes a CPU core when Wireshark or TShark dissects an injected packet or a user opens a crafted capture file; no data access or modification is reported.

CVSS severity7.5
High
EPSS probability3.77%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Infinite-loop denial of service in Wireshark 3.4.0 through 3.4.10 and 3.6.0 allows remote attackers to hang analysis via crafted RTMP data. In rtmpt_get_amf_length, an attacker-controlled 32-bit AMF string or XML length is stored in a signed integer; an underflow can leave rv at zero so the loop condition never clears. The hang consumes a CPU core when Wireshark or TShark dissects an injected packet or a user opens a crafted capture file; no data access or modification is reported.

The record

CVE
CVE-2021-4185
Published
Dec 30, 2021
Updated
Nov 3, 2025
Vendor
Wireshark Foundation
Product
Wireshark
Classifications
CWE-835, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 30, 2021CVE publishedPublication date reported by the CVE source.
  2. Nov 3, 2025Record 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=>=3.4.0, <3.4.10
  2. Affected versionversion==3.6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Wireshark Foundation · Wiresharkversion=>=3.4.0, <3.4.10; version==3.6.0

Published CVSS scores

7.5NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
7.8NISTAV:N/AC:L/Au:N/C:N/I:N/A:C

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 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-835Loop with Unreachable Exit Condition ('Infinite Loop')
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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