CVE-2021-29416Network attack vector

NetNTLM hash disclosure via Swing HTML injection

Published Mar 29, 2021 · Updated Aug 3, 2024

Information disclosure in PortSwigger Burp Suite before 2021.2 allows remote attackers to expose NetNTLM hashes through a malicious request. The Swing-based request viewer renders attacker-supplied HTML and fetches its external resource outside the configured upstream proxy. A user must view the crafted request on Windows, and outbound SMB must be permitted; the resulting authentication attempt discloses the user's NetNTLM hash.

CVSS severity6.5
Medium
EPSS probability1.15%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in PortSwigger Burp Suite before 2021.2 allows remote attackers to expose NetNTLM hashes through a malicious request. The Swing-based request viewer renders attacker-supplied HTML and fetches its external resource outside the configured upstream proxy. A user must view the crafted request on Windows, and outbound SMB must be permitted; the resulting authentication attempt discloses the user's NetNTLM hash.

The record

CVE
CVE-2021-29416
Published
Mar 29, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
T1187
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 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

4.3NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:N
6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/A:N

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

T1187Forced Authentication

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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