Description

A weakness has been identified in a2aproject a2a-java 1.2.0. The affected element is the function BasePushNotificationSender.dispatchNotification of the file server-common/src/main/java/org/a2aproject/sdk/server/tasks/BasePushNotificationSender.java of the component Authorization Header Construction. This manipulation causes http response splitting. The attack can be initiated remotely. Upgrading to version 1.3.0 is sufficient to fix this issue. Patch name: 247a655043f145f6f8e3853724b6a543eaa02001. You should upgrade the affected component.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "7.3",
  "pubDate": "2026-09-14T21:17:42.177Z",
  "pubdate": "2026-09-14T21:17:42.177Z",
  "executiveSummary": "A critical HTTP response splitting vulnerability has been identified in a2aproject a2a-java version 1.2.0, specifically within the authorization header construction logic. This flaw allows a remote, unauthenticated attacker to inject malicious headers or content into the HTTP response stream by manipulating input that is improperly sanitized before being included in the response.\nThe vulnerability resides in the BasePushNotificationSender.dispatchNotification function. Successful exploitation permits an attacker to perform cache poisoning, cross-site scripting (XSS), or session hijacking by forcing the server to return an HTTP response that is misinterpreted by intermediate proxies or the victim's browser.\nGiven that the vulnerability is remotely exploitable without specific privilege requirements, it poses a significant risk to the integrity and confidentiality of communication channels relying on this component. The recommended remediation is an immediate upgrade to version 1.3.0.",
  "technicalDetails": "The root cause of this vulnerability is the failure to validate or sanitize user-supplied input before incorporating it into HTTP headers within the BasePushNotificationSender.dispatchNotification function, located in server-common/src/main/java/org/a2aproject/sdk/server/tasks/BasePushNotificationSender.java.\nHTTP response splitting occurs when an application includes untrusted input in an HTTP header without stripping carriage return (CR, ASCII 0x0D) and line feed (LF, ASCII 0x0A) characters. By injecting these CRLF sequences, an attacker can prematurely terminate the intended header block and insert arbitrary headers or an entirely new HTTP response body.\nThe attack flow begins with the attacker sending a specially crafted request to the application. When the BasePushNotificationSender processes this request, it inserts the malicious, CRLF-laden input into the authorization header. Because the underlying server or the application framework does not enforce strict header formatting, the injected CRLF characters are processed as control characters.\nWhen a web browser or an intermediate proxy (such as a load balancer or a CDN) parses the resulting response, it interprets the attacker-supplied content as a legitimate delimiter. This allows the attacker to force the server to issue a secondary HTTP response. This technique can be leveraged to deliver malicious content to the user's browser, essentially hijacking the response context.\nThe vulnerability is present in version 1.2.0 of a2a-java. Exploitation is remote and does not require pre-existing authentication or elevated privileges, significantly increasing the attack surface. The post-exploitation impact includes the ability to perform cross-site scripting (XSS) if the injected content is reflected back to the user, the ability to overwrite cookies if the attacker injects Set-Cookie headers, or the manipulation of downstream cache nodes to serve malicious payloads to legitimate users.\nRemediation requires applying the patch 247a655043f145f6f8e3853724b6a543eaa02001 by upgrading the component to version 1.3.0, which effectively implements the necessary sanitization logic to strip control characters from header values before they are emitted in the response stream."
}