CVE-2024-7520Public exploitNetwork attack vector

Code execution via WebAssembly subtype confusion

Published Aug 6, 2024 · Updated Mar 24, 2025

WebAssembly type confusion in Firefox before 129, Firefox ESR before 128.1, and Thunderbird before 128.1 allows remote attackers to execute code. During recursive-structure validation, uninitialized supertype vectors compare equal as null, causing incompatible WebAssembly struct fields to pass subtype checks and generate unsafe code. Exploitation requires processing attacker-supplied WebAssembly; Thunderbird disables scripting while reading email, limiting exposure to browser or browser-like contexts.

CVSS severity8.8
High
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

WebAssembly type confusion in Firefox before 129, Firefox ESR before 128.1, and Thunderbird before 128.1 allows remote attackers to execute code. During recursive-structure validation, uninitialized supertype vectors compare equal as null, causing incompatible WebAssembly struct fields to pass subtype checks and generate unsafe code. Exploitation requires processing attacker-supplied WebAssembly; Thunderbird disables scripting while reading email, limiting exposure to browser or browser-like contexts.

The record

CVE
CVE-2024-7520
Published
Aug 6, 2024
Updated
Mar 24, 2025
Vendor
Mozilla
Product
Firefox
Classifications
CWE-94, CWE-843, T1203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 6, 2024CVE publishedPublication date reported by the CVE source.
  2. Mar 24, 2025Record 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=0 <129
  2. Affected versionversion=unspecified <129

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Mozilla · Firefoxversion=0 <129; version=unspecified <129
Mozilla · Thunderbirdversion=0 <128.1; version=unspecified <128.1
Mozilla · Firefox ESRversion=0 <128.1; version=unspecified <128.1

Published CVSS scores

8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
8.8NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:R/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.

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-94Improper Control of Generation of Code ('Code Injection')
CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
T1203Exploitation for Client Execution

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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