Nginx upstream module header line buffer overflow analysis and fix

Vulnerability Key Information Summary 1. Vulnerability Overview Vulnerability Type: Buffer Overflow. Trigger Mechanism: The code contains a length validation check for input data. When the received data length ( ) exceeds the buffer size ( , set to 1024 in the code), the program executes (i.e., returns an error). Risk Point: This logic aims to prevent overflow, but the code comment explicitly states, "If the buffer is too small, we may discard data." This indicates that the handling mechanism may cause legitimate large data packets to be truncated or discarded, leading to Denial of Service (DoS) or data integrity issues. 2. Scope of Impact Affected File: (Upstream processing module). Affected Function: (Processes response header lines). Affected Component: HTTP Upstream Module. 3. Remediation Plan Code Logic: The current defensive programming strategy is to "discard data." Recommendation: It is necessary to confirm whether this module allows for processing response header lines exceeding 1024 bytes. If business logic requires support for longer headers, should be adjusted, or a dynamic memory allocation mechanism should be adopted, rather than simply discarding the data. 4. Key Code Extraction (POC/Logic) The following is the core code snippet regarding buffer overflow handling from the screenshot: ```c / If the buffer is too small, we may discard data. / if (len > buf_size) { return E; // Return error, discard data } / ... / if (len > buf_size) { // Check if it exceeds the buffer ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Another check ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) { // Check again ngx_log_error(NGX_LOG_ERR, r->connection->log, 0, "upstream: header line too long"); return NGX_HTTP_CLIENT_CLOSED_REQUEST; // Return client error } / ... / if (len > buf_size) {

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Nginx upstream module header line buffer overflow analysis and fix

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