CVE-2021-38505Public exploitNetwork attack vector

Copied-secret exposure via missing clipboard exclusions

Published Dec 8, 2021 · Updated Aug 4, 2024

Information exposure in Firefox before 94, Firefox ESR before 91.3, and Thunderbird before 91.3 allows attackers to read copied secrets. Sensitive-copy paths failed to register Windows clipboard exclusion formats, so Clipboard History retained data and Cloud Clipboard synced it. Exposure requires Windows 10 or later with Cloud Clipboard enabled and a user copying data from a protected context such as Private Browsing or a password field.

CVSS severity6.5
Medium
EPSS probability1.05%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Information exposure in Firefox before 94, Firefox ESR before 91.3, and Thunderbird before 91.3 allows attackers to read copied secrets. Sensitive-copy paths failed to register Windows clipboard exclusion formats, so Clipboard History retained data and Cloud Clipboard synced it. Exposure requires Windows 10 or later with Cloud Clipboard enabled and a user copying data from a protected context such as Private Browsing or a password field.

The record

CVE
CVE-2021-38505
Published
Dec 8, 2021
Updated
Aug 4, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-668, T1115
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Dec 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <94

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <94
Mozilla · Thunderbirdversion=unspecified <91.3
Mozilla · Firefox ESRversion=unspecified <91.3

Published CVSS scores

4.3NIST National Vulnerability DatabaseAV:N/AC:M/Au:N/C:P/I:N/A:N
6.5NIST National Vulnerability DatabaseCVSS: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 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-668Exposure of Resource to Wrong Sphere
T1115Clipboard Data

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo