CVE-2026-28367: 
Java vulnerability analysis and mitigation

CVE-2026-28367 is an HTTP request smuggling vulnerability in Red Hat Undertow caused by improper acceptance of \r\r\r as a header block terminator. A remote, unauthenticated attacker can exploit this flaw in conjunction with certain proxy servers — including older versions of Apache Traffic Server and Google Cloud Classic Application Load Balancer — to smuggle malicious HTTP requests. The vulnerability was reported on March 27, 2026, and affects multiple Red Hat products built on Undertow, including JBoss Enterprise Application Platform 7.x/8.x, Fuse 7.0, Single Sign-On 7.0, Data Grid 8.0, Process Automation 7.0, and Apache Camel-based products. It carries a CVSS v3.1 base score of 9.1 (High) (Red Hat CVE, Red Hat Bugzilla).

The root cause is classified as CWE-444 (Inconsistent Interpretation of HTTP Requests / HTTP Request Smuggling). Undertow incorrectly treats the byte sequence \r\r\r as a valid HTTP header block terminator, deviating from RFC-compliant parsing. When a front-end proxy (such as older Apache Traffic Server or Google Cloud Classic Application Load Balancer) forwards this malformed sequence without rejection, an attacker can craft requests that are interpreted differently by the proxy and the Undertow back-end, enabling request smuggling. No authentication or user interaction is required, and the attack is conducted entirely over the network (Red Hat Bugzilla, Red Hat CVE).

Successful exploitation allows a remote attacker to perform HTTP request smuggling, potentially leading to unauthorized access to web requests, manipulation of request content, and bypassing of security controls enforced at the proxy layer. The vulnerability has high confidentiality and integrity impacts — attackers may be able to hijack other users' sessions, poison caches, or access restricted backend resources — though availability is not directly affected. The broad scope of affected Red Hat products (JBoss EAP, Fuse, SSO, Data Grid, and Camel-based platforms) means enterprise environments relying on these stacks in proxy-integrated deployments are at significant risk (Red Hat CVE, Red Hat Bugzilla).

1. Reconnaissance: Identify targets running Undertow-based applications (e.g., JBoss EAP, Red Hat SSO) behind a vulnerable proxy such as an older Apache Traffic Server or Google Cloud Classic Application Load Balancer instance.
2. Craft malformed request: Construct an HTTP request that uses \r\r\r (three carriage returns) as the header block terminator instead of the standard \r\n\r\n.
3. Send to proxy: Transmit the crafted request to the front-end proxy. The proxy, due to its lenient parsing, forwards the malformed sequence to the Undertow back-end.
4. Trigger smuggling: Undertow interprets the \r\r\r sequence as a valid header terminator, causing a desynchronization between the proxy's and back-end's view of the request boundary.
5. Exploit desynchronization: Inject a secondary, hidden HTTP request into the smuggled payload. This hidden request is processed by Undertow as a new, independent request — potentially targeting other users' sessions, bypassing access controls, or poisoning shared caches (Red Hat Bugzilla).

• Network: HTTP requests containing \r\r\r byte sequences in header sections, particularly at positions where \r\n\r\n would normally terminate headers; unexpected or malformed HTTP traffic between proxy and Undertow back-end.
• Logs: Undertow or JBoss EAP access logs showing requests with anomalous header structures or unexpected content-length discrepancies; proxy logs showing forwarded requests with non-standard line endings.
• Application Behavior: Unexpected session behavior such as users receiving responses intended for other users; cache poisoning symptoms (users receiving incorrect cached content); unauthorized access to restricted endpoints without corresponding authentication events.

Red Hat has released patches addressing this vulnerability for JBoss Enterprise Application Platform 8.1 via security advisories RHSA-2026:25126 (platform packages) and RHSA-2026:25125 (RHEL 8/9 packages), published June 10, 2026 (Red Hat Bugzilla). Organizations should upgrade affected Red Hat products to the patched versions as the primary remediation. As a workaround, update front-end proxy servers (Apache Traffic Server, Google Cloud Classic Application Load Balancer) to versions that strictly enforce RFC-compliant HTTP header parsing and reject malformed \r\r\r sequences. Additionally, implement HTTP request validation at the proxy layer and monitor network traffic for suspicious header patterns until patches are fully applied (Red Hat CVE).

The vulnerability received coverage from The Hacker Wire shortly after disclosure, highlighting the request smuggling mechanism via the malformed header terminator (The Hacker Wire). Social media activity was noted on Mastodon via RedPacketSecurity and on Bluesky, indicating moderate community awareness. The vulnerability was tracked by VulDB and radar.offseq.com as part of routine CVE monitoring. No major vendor statements beyond Red Hat's own advisories have been identified.