CVE-2026-84141 in Firefox
Summary
by MITRE • 09/01/2026
Integer overflow in the Graphics: ImageLib component. This vulnerability was fixed in Firefox 155 and Firefox ESR 153.2.
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Analysis
by VulDB Data Team • 09/01/2026
The identified vulnerability resides within the image processing subsystem of Mozilla Firefox, specifically affecting the ImageLib component which is responsible for parsing, decoding, and rendering various graphic formats such as JPEG, PNG, GIF, and WebP. This integer overflow issue arises when the application performs arithmetic operations on values derived from untrusted input data embedded in maliciously crafted image files. In many graphics libraries, dimensions like width and height are read directly from file headers to allocate memory buffers for decoding pixel data. If these header fields contain manipulated or malformed values that exceed expected limits but do not trigger immediate validation checks, subsequent calculations involving multiplication of dimensions by color channel depths can result in an integer overflow. This occurs when the calculated buffer size wraps around a signed 32-bit or 64-bit boundary, resulting in a significantly smaller allocated memory block than what is actually required to hold the decoded image data.
From a technical perspective, this flaw represents a classic CWE-190 Integer Overflow or Wraparound vulnerability. The core issue lies in the lack of rigorous bounds checking before performing arithmetic operations on user-controlled values extracted from external sources. When an attacker constructs a specially designed image file with header fields that cause the multiplication operation to overflow, the application allocates insufficient memory space based on the wrapped-around value. However, subsequent decoding routines proceed under the assumption that sufficient memory has been allocated and attempt to write pixel data into this undersized buffer. This discrepancy between the expected allocation size and the actual available memory leads to a heap-based buffer overread or potentially a heap overflow depending on how the decoder handles out-of-bounds writes relative to adjacent allocations.
The operational impact of exploiting this vulnerability is severe, primarily categorized under CWE-120 Buffer Overflow without null termination if write operations occur, though in many modern browser sandboxing contexts, it often manifests as an out-of-bounds read leading to information disclosure or a denial of service through application crash. If the overflow allows for arbitrary memory writes due to subsequent logic errors, it could potentially lead to remote code execution, although contemporary mitigations such as ASLR and DEP make this path more difficult. The primary immediate risk is stability degradation where visiting a webpage containing the malicious image causes Firefox or its content processes to terminate unexpectedly. Furthermore, if an out-of-bounds read occurs, sensitive memory contents from adjacent heap allocations could be leaked back to the attacker, potentially exposing cryptographic keys, session tokens, or other private data stored in browser memory structures.
This vulnerability aligns with MITRE ATT&CK technique T1203 Exploitation for Client Execution if leveraged via a drive-by download scenario where an image is embedded in a webpage and automatically processed by the victim's browser without explicit user interaction beyond visiting the site. It also relates to T1567 Exfiltration Over Web Protocol if the overflow facilitates data exfiltration through side-channel memory reads. The vulnerability was addressed in Firefox version 155 and Firefox Extended Support Release (ESR) version 153.2, indicating that Mozilla has implemented stricter validation checks for image dimensions and buffer size calculations within the ImageLib component to prevent such arithmetic errors from occurring during the parsing phase of graphic file processing.
To mitigate this risk, users must ensure they are running a patched version of Firefox or any other software utilizing similar graphics libraries by upgrading immediately to version 155 or ESR 153.2 and later updates as they become available. For organizations deploying browsers at scale, it is critical to enforce automated update policies to minimize the window of exposure during which vulnerable versions are in use. Additionally, implementing network-level filtering that blocks suspicious image files from untrusted sources can provide an additional layer of defense against drive-by exploitation attempts. Security teams should also monitor for anomalies in browser process stability and memory usage patterns as indicators of potential exploitation activity targeting this specific component flaw.