CVE-2021-23981Network attack vector

Memory disclosure or crash via unbound WebGL buffer

Published Mar 31, 2021 · Updated Aug 3, 2024

Out-of-bounds read in Mozilla Firefox before 87, Firefox ESR before 78.9, and Thunderbird before 78.9 allows remote attackers to leak memory. The WebGL texture-upload path can skip binding the Pixel Buffer Object used for unpacking, causing ANGLE's LoadRGB8ToBGR565 conversion to read beyond its backing buffer. Exploitation requires user interaction with attacker-controlled WebGL content and can crash the client; ordinary Thunderbird email reading disables scripting.

CVSS severity8.1
High
EPSS probability1.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Out-of-bounds read in Mozilla Firefox before 87, Firefox ESR before 78.9, and Thunderbird before 78.9 allows remote attackers to leak memory. The WebGL texture-upload path can skip binding the Pixel Buffer Object used for unpacking, causing ANGLE's LoadRGB8ToBGR565 conversion to read beyond its backing buffer. Exploitation requires user interaction with attacker-controlled WebGL content and can crash the client; ordinary Thunderbird email reading disables scripting.

The record

CVE
CVE-2021-23981
Published
Mar 31, 2021
Updated
Aug 3, 2024
Vendor
Mozilla
Product
Firefox
Classifications
CWE-787
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 31, 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?

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

  1. Affected versionversion=unspecified <87

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=unspecified <87
Mozilla · Thunderbirdversion=unspecified <78.9
Mozilla · Firefox ESRversion=unspecified <78.9

Published CVSS scores

5.8NIST NVDAV:N/AC:M/Au:N/C:P/I:N/A:P
8.1NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:N/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.

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 exploitUnconfirmed

Weakness, pattern, technique

CWE-787Out-of-bounds Write

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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