CVE-2026-34767: 
JavaScript vulnerability analysis and mitigation

CVE-2026-34767 is an HTTP Response Header Injection vulnerability in the Electron framework affecting apps that register custom protocol handlers via protocol.handle() / protocol.registerSchemesAsPrivileged() or modify response headers via webRequest.onHeadersReceived. When attacker-controlled input is reflected into a response header name or value without sanitization, an attacker can inject additional response headers. The vulnerability was published on April 2–3, 2026, and affects Electron versions below 38.8.6, 39.x before 39.8.3, 40.x before 40.8.3, and 41.x before 41.0.3. It carries a CVSS v3.1 base score of 5.9 (Moderate) per the GitHub Advisory (GitHub Advisory, Electron Advisory).

The root cause is improper neutralization of CRLF sequences in HTTP headers (CWE-113) and more broadly improper neutralization of special elements in output used by a downstream component (CWE-74). When an Electron app reflects external, attacker-influenced data into HTTP response headers — either through custom protocol handler responses or via the webRequest.onHeadersReceived API — without stripping or encoding carriage return (\r) and line feed (\n) characters, an attacker can terminate the current header and inject arbitrary new headers into the response. This class of attack (HTTP Response Splitting / CAPEC-34) allows manipulation of the response structure as interpreted by the Electron renderer process. Apps that do not incorporate external input into response headers are not affected (GitHub Advisory, Electron Advisory).

Successful exploitation allows an attacker to inject arbitrary HTTP response headers into responses processed by the Electron app's renderer, enabling manipulation of cookies (e.g., setting or overwriting session cookies), bypassing or weakening Content Security Policy (CSP), and undermining cross-origin access controls. The integrity impact is rated High, with a low confidentiality impact, and no availability impact. Exploitation is conditional on the app reflecting attacker-controlled input into response headers and requires user interaction, limiting the attack surface to specific application configurations (GitHub Advisory, Electron Advisory).

No public proof-of-concept exploit code or evidence of in-the-wild exploitation has been reported for CVE-2026-34767. The EPSS score is approximately 0.013% (2nd percentile), indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been identified (GitHub Advisory).

1. Identify a vulnerable Electron app: Locate an Electron application (versions below 38.8.6, 39.8.3, 40.8.3, or 41.0.3) that uses protocol.handle(), protocol.registerSchemesAsPrivileged(), or webRequest.onHeadersReceived and reflects user-supplied or externally-sourced data into HTTP response headers.
2. Craft a malicious input: Prepare input containing CRLF sequences (e.g., \r\n) followed by a crafted header, such as injected-header: malicious-value\r\nSet-Cookie: session=attacker-controlled.
3. Deliver the payload: Cause the vulnerable app to process the crafted input — for example, by supplying a URL parameter, file name, or other user-controlled value that the app incorporates into a response header without sanitization.
4. Trigger header injection: The Electron framework passes the unsanitized value into the HTTP response, causing the renderer to interpret the injected content as additional response headers.
5. Achieve objective: Depending on the injected headers, the attacker may set or overwrite cookies, disable or bypass CSP directives, or manipulate cross-origin access controls to facilitate further attacks such as session hijacking or cross-site scripting (GitHub Advisory, Electron Advisory).

• Logs: Unexpected or malformed HTTP response headers in Electron app debug logs or network traffic captures, particularly headers containing CRLF sequences or unexpected Set-Cookie, Content-Security-Policy, or Access-Control-Allow-Origin values.
• Network: Anomalous response headers observed in traffic between the Electron renderer and custom protocol handlers, especially headers not expected by the application's normal operation.
• Application Behavior: Unexpected changes to cookie values, CSP violations logged in the renderer console, or cross-origin requests succeeding where they should be blocked.

Electron has released patched versions addressing this vulnerability: 38.8.6, 39.8.3, 40.8.3, and 41.0.3. Developers should upgrade to the appropriate fixed version as the primary remediation. As a workaround for apps that cannot immediately upgrade, all untrusted or externally-sourced input must be validated and sanitized — specifically stripping or rejecting CRLF characters — before including it in any response header name or value. Apps that do not reflect external input into response headers are not affected and require no action (GitHub Advisory, Electron Advisory).

The advisory was published by Electron maintainer VerteDinde on April 2, 2026, and subsequently picked up by standard vulnerability tracking feeds. IBM issued a security bulletin in May 2026 noting that MongoDB Enterprise Advanced (with IBM) is also affected by this CVE among others (IBM Advisory). No significant independent researcher commentary or broad media coverage has been identified beyond routine vulnerability database entries.