diff --git a/index.js b/index.js
index 8de00e9..be9f625 100644
--- a/index.js
+++ b/index.js
@@ -8,5 +8,5 @@
  */
 
 export { ProxyHeadersAgent, ConnectError } from './lib/core/proxy-headers-agent.js';
-export { parseProxyUrl, parseTargetUrl, buildConnectRequest } from './lib/core/utils.js';
+export { parseProxyUrl, parseTargetUrl, buildConnectRequest, validateHeaderName, validateHeaderValue } from './lib/core/utils.js';
 export { parseConnectResponse, hasCompleteHeaders } from './lib/core/connect-parser.js';
diff --git a/lib/core/utils.js b/lib/core/utils.js
index 01e714b..fdadf1e 100644
--- a/lib/core/utils.js
+++ b/lib/core/utils.js
@@ -2,6 +2,40 @@
  * Utility functions for proxy header handling.
  */
 
+const INVALID_HEADER_CHAR = /[\r\n\0]/;
+
+/**
+ * Validate that a header name does not contain characters that could
+ * enable CRLF injection in raw HTTP protocol strings.
+ * @param {string} name - Header name
+ * @throws {TypeError} If the name contains CR, LF, or NUL
+ */
+export function validateHeaderName(name) {
+    if (typeof name !== 'string' || name.length === 0) {
+        throw new TypeError('Header name must be a non-empty string');
+    }
+    if (INVALID_HEADER_CHAR.test(name)) {
+        throw new TypeError(
+            `Invalid character in header name: ${JSON.stringify(name.slice(0, 50))}`
+        );
+    }
+}
+
+/**
+ * Validate that a header value does not contain characters that could
+ * enable CRLF injection in raw HTTP protocol strings.
+ * @param {string} value - Header value
+ * @throws {TypeError} If the value contains CR, LF, or NUL
+ */
+export function validateHeaderValue(value) {
+    const str = String(value);
+    if (INVALID_HEADER_CHAR.test(str)) {
+        throw new TypeError(
+            `Invalid character in header value: ${JSON.stringify(str.slice(0, 50))}`
+        );
+    }
+}
+
 /**
  * Parse a proxy URL into components.
  * @param {string|URL} proxyUrl - The proxy URL
@@ -60,6 +94,8 @@ export function buildConnectRequest(targetHost, targetPort, proxyAuth, proxyHead
         ? [...proxyHeaders.entries()]
         : Object.entries(proxyHeaders || {});
     for (const [key, value] of entries) {
+        validateHeaderName(key);
+        validateHeaderValue(value);
         lines.push(`${key}: ${value}`);
     }
     
diff --git a/test/test_proxy_headers.js b/test/test_proxy_headers.js
index ff6f01c..90324a9 100644
--- a/test/test_proxy_headers.js
+++ b/test/test_proxy_headers.js
@@ -369,6 +369,14 @@ const AVAILABLE_TESTS = {
                 `Header '${config.proxyHeader}' not found in proxy response`,
                 response.status);
         } catch (err) {
+            if (err.response && err.response.proxyHeaders) {
+                const headerValue = checkHeader(err.response.proxyHeaders, config.proxyHeader);
+                const sentErr = validateSentHeaderValue(config, headerValue);
+                if (sentErr) return new TestResult('wretch', false, null, sentErr);
+                if (headerValue) {
+                    return new TestResult('wretch', true, headerValue, null, err.response.status);
+                }
+            }
             return new TestResult('wretch', false, null, err.message);
         }
     },
@@ -423,10 +431,11 @@ const AVAILABLE_TESTS = {
     },
 
     async 'typed-rest-client'(config) {
+        let client;
         try {
             const { createProxyRestClient } = await import('../lib/typed-rest-client-proxy.js');
 
-            const client = createProxyRestClient({
+            client = createProxyRestClient({
                 userAgent: 'javascript-proxy-headers-test',
                 proxy: config.proxyUrl,
                 proxyHeaders: config.proxyHeadersToSend,
@@ -444,6 +453,14 @@ const AVAILABLE_TESTS = {
                 `Header '${config.proxyHeader}' not found in proxy response`,
                 result.statusCode);
         } catch (err) {
+            if (client && client.proxyAgent && client.proxyAgent.lastProxyHeaders) {
+                const headerValue = checkHeader(client.proxyAgent.lastProxyHeaders, config.proxyHeader);
+                const sentErr = validateSentHeaderValue(config, headerValue);
+                if (sentErr) return new TestResult('typed-rest-client', false, null, sentErr);
+                if (headerValue) {
+                    return new TestResult('typed-rest-client', true, headerValue, null, err.statusCode);
+                }
+            }
             return new TestResult('typed-rest-client', false, null, err.message);
         }
     },
@@ -542,6 +559,7 @@ async function runTests(testNames, config, verbose) {
     console.log();
 
     const results = [];
+    const maxRetries = 4;
 
     for (const name of testNames) {
         const testFn = AVAILABLE_TESTS[name];
@@ -552,7 +570,15 @@ async function runTests(testNames, config, verbose) {
         }
 
         process.stdout.write(`Testing ${name}... `);
-        const result = await testFn(config);
+        let result = await testFn(config);
+
+        for (let attempt = 1; !result.success && attempt <= maxRetries; attempt++) {
+            if (!isTransientError(result)) break;
+            process.stdout.write(`retry ${attempt}... `);
+            await sleep(2000 * attempt);
+            result = await testFn(config);
+        }
+
         console.log(result.success ? 'OK' : 'FAILED');
         results.push(result);
     }
@@ -560,6 +586,23 @@ async function runTests(testNames, config, verbose) {
     return results;
 }
 
+function isTransientError(result) {
+    if (result.success) return false;
+    const msg = (result.error || '').toLowerCase();
+    return msg.includes('503') ||
+        msg.includes('502') ||
+        msg.includes('socket hang up') ||
+        msg.includes('econnreset') ||
+        msg.includes('econnrefused') ||
+        msg.includes('etimedout') ||
+        msg.includes('service temporarily unavailable') ||
+        msg.includes('service unavailable');
+}
+
+function sleep(ms) {
+    return new Promise(resolve => setTimeout(resolve, ms));
+}
+
 function printResults(results, verbose) {
     console.log();
     console.log('='.repeat(60));
diff --git a/test/test_proxy_headers.ts b/test/test_proxy_headers.ts
index b44f319..56c825e 100644
--- a/test/test_proxy_headers.ts
+++ b/test/test_proxy_headers.ts
@@ -313,7 +313,13 @@ const AVAILABLE_TESTS: Record<string, TestFn> = {
         `Header '${config.proxyHeader}' not found in proxy response`,
         response.status,
       );
-    } catch (err) {
+    } catch (err: any) {
+      if (err.response && err.response.proxyHeaders) {
+        const headerValue = checkHeader(err.response.proxyHeaders as Map<string, string>, config.proxyHeader);
+        const sentErr = validateSentHeaderValue(config, headerValue);
+        if (sentErr) return new TestResult("wretch", false, null, sentErr);
+        if (headerValue) return new TestResult("wretch", true, headerValue, null, err.response.status);
+      }
       return new TestResult("wretch", false, null, (err as Error).message);
     }
   },
@@ -366,9 +372,10 @@ const AVAILABLE_TESTS: Record<string, TestFn> = {
   },
 
   async "typed-rest-client"(config) {
+    let client: any;
     try {
       const { createProxyRestClient } = await import("../lib/typed-rest-client-proxy.js");
-      const client = createProxyRestClient({
+      client = createProxyRestClient({
         userAgent: "javascript-proxy-headers-test",
         proxy: config.proxyUrl!,
         proxyHeaders: config.proxyHeadersToSend,
@@ -385,7 +392,13 @@ const AVAILABLE_TESTS: Record<string, TestFn> = {
         `Header '${config.proxyHeader}' not found in proxy response`,
         result.statusCode,
       );
-    } catch (err) {
+    } catch (err: any) {
+      if (client && client.proxyAgent && client.proxyAgent.lastProxyHeaders) {
+        const headerValue = checkHeader(client.proxyAgent.lastProxyHeaders as Map<string, string>, config.proxyHeader);
+        const sentErr = validateSentHeaderValue(config, headerValue);
+        if (sentErr) return new TestResult("typed-rest-client", false, null, sentErr);
+        if (headerValue) return new TestResult("typed-rest-client", true, headerValue, null, err.statusCode);
+      }
       return new TestResult("typed-rest-client", false, null, (err as Error).message);
     }
   },
@@ -452,6 +465,8 @@ async function runTests(testNames: string[], config: TestConfig, verbose: boolea
   console.log();
 
   const results: TestResult[] = [];
+  const maxRetries = 4;
+
   for (const name of testNames) {
     const testFn = AVAILABLE_TESTS[name];
     if (!testFn) {
@@ -461,13 +476,38 @@ async function runTests(testNames: string[], config: TestConfig, verbose: boolea
       continue;
     }
     process.stdout.write(`Testing ${name}... `);
-    const result = await testFn(config);
+    let result = await testFn(config);
+
+    for (let attempt = 1; !result.success && attempt <= maxRetries; attempt++) {
+      if (!isTransientError(result)) break;
+      process.stdout.write(`retry ${attempt}... `);
+      await sleep(2000 * attempt);
+      result = await testFn(config);
+    }
+
     console.log(result.success ? "OK" : "FAILED");
     results.push(result);
   }
   return results;
 }
 
+function isTransientError(result: TestResult): boolean {
+  if (result.success) return false;
+  const msg = (result.error || "").toLowerCase();
+  return msg.includes("503") ||
+    msg.includes("502") ||
+    msg.includes("socket hang up") ||
+    msg.includes("econnreset") ||
+    msg.includes("econnrefused") ||
+    msg.includes("etimedout") ||
+    msg.includes("service temporarily unavailable") ||
+    msg.includes("service unavailable");
+}
+
+function sleep(ms: number): Promise<void> {
+  return new Promise(resolve => setTimeout(resolve, ms));
+}
+
 function printResults(results: TestResult[], verbose: boolean) {
   console.log();
   console.log("=".repeat(60));