CVE-2026-77682
Description
A code injection vulnerability exists in Epiphany when the user invokes form autofill from the context menu on a page containing a malicious HTML form.
In embed/web-process-extension/resources/js/ephy_autofill.js, getSelector() builds a CSS selector by directly interpolating an element's id attribute:
path.unshift(`#${el.id}`);
When the user selects an autofill entry, the browser process in embed/ephy-web-view.c previously constructed JavaScript using sprintf with the selector embedded in single quotes:
EphyAutofill.fill(PAGE_ID, 'SELECTOR', FILL_CHOICE);
Because SELECTOR comes from attacker-controlled page content and is not escaped, a crafted id such as a'); PAYLOAD; var _=(' breaks out of the string literal and executes arbitrary JavaScript when the script is evaluated.
The injected code runs in Epiphany's private autofill script world, which hosts EphyAutofill credential APIs and password manager save/request handlers. The reporter demonstrated a proof of concept that injects credentials into another domain and uses Ephy.permissionsManager to enumerate domains with special permissions. Full exfiltration of all saved passwords was not demonstrated but may be possible given the privileges of this context.
Exploitation requires the victim to visit a malicious page, right-click on a form field, and choose an Autofill context menu item. This is a deliberate user action but does not require installing software or entering credentials manually.
Affected versions: Epiphany >= 47.beta. Fixed upstream in epiphany 50.6 and 49.9 via merge request !2147, which replaces sprintf-based script evaluation with a WebKit user message and jsc_value_object_invoke_method() passing the selector as a typed string argument. Upstream report: https://gitlab.gnome.org/GNOME/epiphany/-/issues/2921
Statement
A code injection flaw was found in Epiphany's autofill handling. A malicious website could craft an HTML element id that, when used to build a CSS selector for autofill, caused attacker-controlled JavaScript to execute in Epiphany's privileged autofill context. If a victim triggered form autofill from the context menu on such a page, an attacker could access autofill and password manager functionality beyond normal web page restrictions, potentially exposing saved credentials or manipulating autofill behavior across sites.
Mitigation
Upgrade to epiphany 50.6, 49.9, or later. Until patched, avoid using the Autofill context menu on untrusted websites.
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
In some cases, injectable code controls authentication; this may lead to a remote vulnerability.
Access Control
Technical Impact: Gain Privileges or Assume Identity
Injected code can access resources that the attacker is directly prevented from accessing.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. As a result, code injection can often result in the execution of arbitrary code. Code injection attacks can also lead to loss of data integrity in nearly all cases, since the control-plane data injected is always incidental to data recall or writing.
Non-Repudiation
Technical Impact: Hide Activities
Often the actions performed by injected control code are unlogged.
Acknowledgements
Red Hat would like to thank Fernando Munoz for reporting this issue.
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