Firefox <149 Sandbox Escape: XPCOM Integer Overflow
CVE-2026-4689 Published on March 24, 2026
Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component
Sandbox escape due to incorrect boundary conditions, integer overflow in the XPCOM component. This vulnerability was fixed in Firefox 149, Firefox ESR 115.34, Firefox ESR 140.9, Thunderbird 149, and Thunderbird 140.9.
Vulnerability Analysis
CVE-2026-4689 can be exploited with network access, requires user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Types
What is a Classic Buffer Overflow Vulnerability?
The program copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. A buffer overflow condition exists when a program attempts to put more data in a buffer than it can hold, or when a program attempts to put data in a memory area outside of the boundaries of a buffer. The simplest type of error, and the most common cause of buffer overflows, is the "classic" case in which the program copies the buffer without restricting how much is copied. Other variants exist, but the existence of a classic overflow strongly suggests that the programmer is not considering even the most basic of security protections.
CVE-2026-4689 has been classified to as a Classic Buffer Overflow vulnerability or weakness.
Integer Overflow or Wraparound
The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. An integer overflow or wraparound occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may wrap to become a very small or negative number. While this may be intended behavior in circumstances that rely on wrapping, it can have security consequences if the wrap is unexpected. This is especially the case if the integer overflow can be triggered using user-supplied inputs. This becomes security-critical when the result is used to control looping, make a security decision, or determine the offset or size in behaviors such as memory allocation, copying, concatenation, etc.
Products Associated with CVE-2026-4689
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Affected Versions
Mozilla Firefox:- Version 115.34, <= 115.* is unaffected.
- Version 140.9, <= 140.* is unaffected.
- Version 149, <= * is unaffected.
- Version 140.9, <= 140.* is unaffected.
- Version 149, <= * is unaffected.
- Version 0:140.9.0-1.el10_1 and below * is unaffected.
- Version 0:140.9.0-1.el10_1 and below * is unaffected.
- Version 0:140.9.0-1.el10_0 and below * is unaffected.
- Version 0:140.9.0-1.el10_0 and below * is unaffected.
- Version 0:140.9.0-1.el7_9 and below * is unaffected.
- Version 0:140.9.0-1.el8_10 and below * is unaffected.
- Version 0:140.9.0-1.el8_10 and below * is unaffected.
- Version 0:140.9.0-1.el8_2 and below * is unaffected.
- Version 0:140.9.0-1.el8_2 and below * is unaffected.
- Version 0:140.9.0-1.el8_4 and below * is unaffected.
- Version 0:140.9.0-1.el8_4 and below * is unaffected.
- Version 0:140.9.0-1.el8_4 and below * is unaffected.
- Version 0:140.9.0-1.el8_4 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_6 and below * is unaffected.
- Version 0:140.9.0-1.el8_8 and below * is unaffected.
- Version 0:140.9.0-1.el8_8 and below * is unaffected.
- Version 0:140.9.0-1.el8_8 and below * is unaffected.
- Version 0:140.9.0-1.el8_8 and below * is unaffected.
- Version 0:140.9.0-1.el9_7 and below * is unaffected.
- Version 0:140.9.0-1.el9_7 and below * is unaffected.
- Version 0:140.9.0-1.el9_0 and below * is unaffected.
- Version 0:140.9.0-1.el9_0 and below * is unaffected.
- Version 0:140.9.0-1.el9_2 and below * is unaffected.
- Version 0:140.9.0-1.el9_2 and below * is unaffected.
- Version 0:140.9.0-1.el9_4 and below * is unaffected.
- Version 0:140.9.0-1.el9_4 and below * is unaffected.
- Version 0:140.9.0-1.el9_6 and below * is unaffected.
- Version 0:140.9.0-1.el9_6 and below * is unaffected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.