CVE-2026-32881 in ewe
Summary
by MITRE • 03/20/2026
ewe is a Gleam web server. ewe is a Gleam web server. Versions 0.6.0 through 3.0.4 are vulnerable to authentication bypass or spoofed proxy-trust headers. Chunked transfer encoding trailer handling merges declared trailer fields into req.headers after body parsing, but the denylist only blocks 9 header names. A malicious client can exploit this by declaring these headers in the Trailer field and appending them after the final chunk, causing request.set_header to overwrite legitimate values (e.g., those set by a reverse proxy). This enables attackers to forge authentication credentials, hijack sessions, bypass IP-based rate limiting, or spoof proxy-trust headers in any downstream middleware that reads headers after ewe.read_body is called. This issue has been fixed in version 3.0.5.
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Analysis
by VulDB Data Team • 03/25/2026
The vulnerability identified as CVE-2026-32881 affects the ewe web server implementation written in Gleam, a functional programming language for building distributed systems. This issue manifests as an authentication bypass and proxy-trust header spoofing vulnerability that exists in versions 0.6.0 through 3.0.4 of the software. The core problem stems from improper handling of chunked transfer encoding trailer fields within the request processing pipeline, creating a critical security gap that can be exploited by malicious actors to manipulate request headers.
The technical flaw occurs during the processing of HTTP requests that utilize chunked transfer encoding with trailers. When a client sends a request with chunked encoding, it can include trailer fields that are sent after the final chunk of data. The ewe server implementation parses the request body first and then processes trailer fields, but the security mechanism that should prevent header manipulation only blocks nine specific header names from being set through trailers. This partial denylist approach creates an exploitable gap since there are numerous HTTP headers that can be manipulated to achieve malicious objectives. The vulnerability specifically allows attackers to use the Trailer field to append header names that are not properly filtered, enabling the request.set_header function to overwrite legitimate header values that would typically be set by reverse proxies or other middleware components.
The operational impact of this vulnerability extends far beyond simple header manipulation, creating multiple attack vectors that can compromise system security. An attacker can exploit this flaw to forge authentication credentials by overwriting authorization headers, effectively bypassing authentication mechanisms. Session hijacking becomes possible when attacker-controlled headers overwrite session identifiers or other session-related metadata. Additionally, the vulnerability enables IP-based rate limiting bypass, allowing malicious actors to circumvent traffic control measures that are meant to prevent abuse. The most concerning aspect is that this vulnerability can be leveraged to spoof proxy-trust headers, which means that downstream middleware components that depend on legitimate proxy headers for security decisions can be deceived. This creates a cascading effect where security controls that rely on proper header values become ineffective, potentially allowing attackers to gain unauthorized access to protected resources or escalate privileges within the system.
This vulnerability aligns with CWE-295 which addresses improper certificate validation, and more specifically relates to CWE-284 which covers improper access control. The attack pattern follows the MITRE ATT&CK framework's technique T1078 for valid accounts and T1566 for credential harvesting through manipulation of authentication mechanisms. The exploitation technique involves header injection and manipulation that can be categorized under T1562.001 for disabling security tools and T1071.004 for application layer protocol manipulation. Organizations using affected versions of ewe should immediately upgrade to version 3.0.5 to remediate this vulnerability, as the fix addresses the incomplete denylist implementation by expanding the header filtering mechanism to properly block all potentially dangerous headers that could be used for header manipulation attacks. The fix ensures that all header names that could compromise security are properly filtered during the processing of chunked transfer encoding trailers, preventing the overwriting of legitimate header values that are essential for maintaining proper authentication and access control within the system.