diff --git a/src/lib/server/logging/redaction.test.ts b/src/lib/server/logging/redaction.test.ts
index 2857565c..fe9292cb 100644
--- a/src/lib/server/logging/redaction.test.ts
+++ b/src/lib/server/logging/redaction.test.ts
@@ -1,4 +1,7 @@
 import pino from 'pino';
+import http from 'node:http';
+import type { AddressInfo } from 'node:net';
+import { S3Client, ListBucketsCommand } from '@aws-sdk/client-s3';
 import { Writable } from 'node:stream';
 import { describe, it, expect } from 'vitest';
 import { redactionPaths, redactionCensor } from './redaction.js';
@@ -84,6 +87,85 @@ describe('redaction', () => {
     expect(parsed.req.headers['set-cookie']).toBe('[Redacted]');
   });
 
+  it('redacts the storage connection header, which carries the S3 secret key', () => {
+    const { log, lines } = createTestLogger();
+    const header = btoa(
+      JSON.stringify({ type: 's3', credentials: { accessKey: 'AK', secretKey: 'SK-CANARY' } })
+    );
+    log.info({ req: { headers: { 'x-storage-connection': header } } }, 'test');
+    log.flush();
+
+    expect(lines[0]).not.toContain(header);
+    expect(JSON.parse(lines[0]).req.headers['x-storage-connection']).toBe('[Redacted]');
+  });
+
+  it('redacts the storage connection header on a bare headers object', () => {
+    const { log, lines } = createTestLogger();
+    const header = btoa(JSON.stringify({ credentials: { secretKey: 'SK-CANARY' } }));
+    log.info({ headers: { 'x-storage-connection': header } }, 'test');
+    log.flush();
+
+    expect(lines[0]).not.toContain(header);
+    expect(JSON.parse(lines[0]).headers['x-storage-connection']).toBe('[Redacted]');
+  });
+
+  it('redacts the credential material an S3 endpoint echoes back', async () => {
+    const server = http.createServer((_req, res) => {
+      res.writeHead(403, { 'Content-Type': 'application/xml' });
+      res.end(
+        `<?xml version="1.0" encoding="UTF-8"?><Error>` +
+          `<Code>SignatureDoesNotMatch</Code><Message>mismatch</Message>` +
+          `<AWSAccessKeyId>AKIA-CANARY</AWSAccessKeyId>` +
+          `<StringToSign>STS-CANARY</StringToSign>` +
+          `<SignatureProvided>SIG-CANARY</SignatureProvided>` +
+          `<CanonicalRequest>CR-CANARY</CanonicalRequest>` +
+          `</Error>`
+      );
+    });
+    await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve));
+    const { port } = server.address() as AddressInfo;
+
+    const client = new S3Client({
+      region: 'eu-central-1',
+      endpoint: `http://127.0.0.1:${port}`,
+      forcePathStyle: true,
+      credentials: { accessKeyId: 'AKIA-CANARY', secretAccessKey: 'x' },
+      maxAttempts: 1
+    });
+
+    const { log, lines } = createTestLogger();
+    try {
+      await client.send(new ListBucketsCommand({}));
+      throw new Error('expected the request to fail');
+    } catch (err) {
+      log.warn({ err }, 'storage connection test failed');
+    } finally {
+      client.destroy();
+      await new Promise<void>((resolve) => server.close(() => resolve()));
+    }
+    log.flush();
+
+    const line = lines[0];
+    expect(line).not.toContain('AKIA-CANARY');
+    expect(line).not.toContain('STS-CANARY');
+    expect(line).not.toContain('SIG-CANARY');
+    expect(line).not.toContain('CR-CANARY');
+
+    // The diagnostics support actually needs must survive.
+    const parsed = JSON.parse(line);
+    expect(parsed.err.name).toBe('SignatureDoesNotMatch');
+    expect(parsed.err.$metadata.httpStatusCode).toBe(403);
+  }, 20000);
+
+  it('redacts echoed credentials nested in aggregated errors', () => {
+    const { log, lines } = createTestLogger();
+    const inner = Object.assign(new Error('inner'), { AWSAccessKeyId: 'AKIA-CANARY' });
+    log.warn({ err: new AggregateError([inner], 'all failed') }, 'test');
+    log.flush();
+
+    expect(lines[0]).not.toContain('AKIA-CANARY');
+  });
+
   it('does not redact safe fields', () => {
     const { log, lines } = createTestLogger();
     log.info({ user_id: 'u123', path: '/api/test' }, 'test');
diff --git a/src/lib/server/logging/redaction.ts b/src/lib/server/logging/redaction.ts
index 1136d666..1b5ed98c 100644
--- a/src/lib/server/logging/redaction.ts
+++ b/src/lib/server/logging/redaction.ts
@@ -1,9 +1,28 @@
+const s3ErrorCredentialFields = [
+  'AWSAccessKeyId',
+  'StringToSign',
+  'StringToSignBytes',
+  'CanonicalRequest',
+  'CanonicalRequestBytes',
+  'SignatureProvided'
+];
+
+const s3ErrorPaths = s3ErrorCredentialFields.flatMap((field) => [
+  `*.${field}`,
+  `err.aggregateErrors[*].${field}`
+]);
+
 /** Pino redaction paths for sensitive fields. */
 export const redactionPaths: string[] = [
+  // S3 error bodies echoed back by the remote endpoint
+  ...s3ErrorPaths,
+
   // Request headers
   'req.headers.authorization',
   'req.headers.cookie',
   'req.headers["set-cookie"]',
+  // Carries the base64 JSON S3 connection config, including secretKey.
+  'req.headers["x-storage-connection"]',
 
   // Token/credential fields (exact)
   'accessToken',
@@ -22,6 +41,7 @@ export const redactionPaths: string[] = [
   '*.authorization',
   '*.cookie',
   '*.set-cookie',
+  '*["x-storage-connection"]',
   '*.accessToken',
   '*.refreshToken',
   '*.idToken',