CVE-2026-100823 Overview
CVE-2026-100823 is a spoofing vulnerability in the Downloads component of Firefox for Android. The flaw allows a remote attacker to manipulate download-related user interface elements to mislead the user about the origin, name, or nature of a downloaded file. Exploitation requires user interaction, such as visiting a crafted web page and initiating a download. Mozilla addressed the issue in Firefox 157.
Critical Impact
An attacker-controlled web page can spoof download metadata in Firefox for Android, tricking users into trusting or executing malicious files delivered through the browser.
Affected Products
- Mozilla Firefox for Android versions prior to 157
Discovery Timeline
- 2026-09-29 - CVE-2026-100823 published to NVD
- 2026-09-30 - Last updated in NVD database
Technical Details for CVE-2026-100823
Vulnerability Analysis
The vulnerability resides in the Downloads component of Firefox for Android. A malicious website can influence how download information is presented to the user in the browser interface. This creates a mismatch between what the user sees and the actual file being fetched or saved. Because the spoof occurs inside a trusted browser surface, users have limited ability to detect the manipulation.
The attack requires the victim to interact with a crafted page and proceed through a download prompt. Successful exploitation does not grant code execution, but it does undermine the integrity of file origin indicators that users rely on. This class of issue maps to user interface confusion and mobile app spoofing weaknesses.
Root Cause
The root cause is improper validation or presentation of download metadata within the Firefox for Android Downloads component. Refer to Mozilla Bug Report #2054384 and Mozilla Security Advisory MFSA-2026-97 for the vendor's technical details.
Attack Vector
The attack is delivered over the network. A remote attacker hosts a malicious page that a Firefox for Android user visits. The page issues a download that leverages the spoofing weakness to misrepresent the file to the user. No authentication is required, but the user must engage with the download flow.
No verified proof-of-concept code is publicly available. See the referenced Mozilla advisory for exploitation context.
Detection Methods for CVE-2026-100823
Indicators of Compromise
- Firefox for Android installations reporting version numbers below 157 in mobile device management (MDM) inventory.
- Downloaded files on Android devices whose declared MIME type, extension, or displayed origin does not match the actual server response captured in network logs.
- User reports of files that appear to originate from trusted sites but resolve to unrelated third-party domains.
Detection Strategies
- Correlate mobile browser telemetry with proxy or DNS logs to flag downloads where the visible source domain differs from the resolved network destination.
- Inspect Android endpoint logs for newly written files in the Firefox downloads directory that lack expected provenance metadata.
- Monitor phishing infrastructure feeds for pages known to abuse browser download spoofing techniques.
Monitoring Recommendations
- Track Firefox for Android version distribution across managed devices and alert when versions below 157 remain in use.
- Enable mobile threat defense to inspect files delivered through browser downloads before they execute or are shared.
- Review user-submitted phishing reports for patterns involving Firefox on Android and unexpected download prompts.
How to Mitigate CVE-2026-100823
Immediate Actions Required
- Update Firefox for Android to version 157 or later through Google Play or the Mozilla distribution channel.
- Push the updated Firefox package to managed Android fleets using MDM policies with a defined enforcement deadline.
- Advise users to verify download sources through address bar indicators and to avoid opening unexpected files delivered by web pages.
Patch Information
Mozilla fixed CVE-2026-100823 in Firefox 157. Details are published in Mozilla Security Advisory MFSA-2026-97, with the underlying issue tracked in Mozilla Bug Report #2054384.
Workarounds
- Restrict use of Firefox for Android on managed devices until the patched version is deployed.
- Route mobile browser traffic through a filtering proxy that blocks known malicious download sources.
- Disable or discourage file downloads within Firefox for Android for high-risk user groups until updates are confirmed.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
