diff --git a/backend/src/workspaces/schema.ts b/backend/src/workspaces/schema.ts
index 47beb0b9..acd635cd 100644
--- a/backend/src/workspaces/schema.ts
+++ b/backend/src/workspaces/schema.ts
@@ -276,6 +276,7 @@ function isSafeEvidencePattern(value: string): boolean {
 }
 
 function parsePublicHttpUri(value: string): URL | undefined {
+  if (value.trim() !== value || /[\u0000-\u001f\u007f\\]/u.test(value)) return undefined;
   try {
     const parsed = new URL(value);
     if (
@@ -297,14 +298,20 @@ function canonicalPublicHttpUri(value: string): string | undefined {
 }
 
 function isSafeS3Uri(value: string): boolean {
+  if (value.trim() !== value || /[\u0000-\u001f\u007f\\]/u.test(value)) return false;
   try {
     const parsed = new URL(value);
+    const bucket = parsed.hostname;
+    const validBucket = /^(?=.{3,63}$)(?!-)(?!.*\.\.)(?!.*\.-)(?!.*-\.)[a-z0-9](?:[a-z0-9.-]*[a-z0-9])?$/.test(bucket)
+      && !/^\d{1,3}(?:\.\d{1,3}){3}$/.test(bucket);
     return parsed.protocol === "s3:"
-      && parsed.hostname.length > 0
+      && validBucket
+      && parsed.port === ""
       && parsed.username === ""
       && parsed.password === ""
       && parsed.search === ""
-      && parsed.hash === "";
+      && parsed.hash === ""
+      && parsed.href === value;
   } catch {
     return false;
   }
@@ -380,7 +387,8 @@ const s3EvidenceSourceSchema = z.object({
       message: "custom S3 endpoints must be explicitly trusted",
     });
   }
-  if (source.endpoint_url.startsWith("http:") && !source.allow_insecure_endpoint) {
+  const endpoint = parsePublicHttpUri(source.endpoint_url);
+  if (endpoint?.protocol === "http:" && !source.allow_insecure_endpoint) {
     context.addIssue({
       code: "custom", path: ["allow_insecure_endpoint"],
       message: "HTTP S3 endpoints require an explicit insecure opt-in",
diff --git a/backend/test/workspaces-schema.test.ts b/backend/test/workspaces-schema.test.ts
index fa53bf81..2b6f971f 100644
--- a/backend/test/workspaces-schema.test.ts
+++ b/backend/test/workspaces-schema.test.ts
@@ -476,6 +476,7 @@ const invalidHttpUris = [
   "https://example.com/manifest?token=CANARY-HTTP",
   "https://example.com/manifest#CANARY-HTTP",
   "ftp://example.com/manifest/CANARY-HTTP",
+  "\nhttps://example.com/CANARY-HTTP",
 ];
 
 test.each(invalidHttpUris)("rejects unsafe HTTP descriptor URI %# without leaking it", (uri) => {
@@ -506,6 +507,8 @@ test.each(invalidHttpBounds)("rejects invalid HTTP bound %s=%s", (field, value)
 const invalidS3Uris = [
   "https://bucket/prefix", "s3:///prefix", "s3://user:CANARY-S3@bucket/prefix",
   "s3://bucket/prefix?token=CANARY-S3", "s3://bucket/prefix#CANARY-S3",
+  "s3://bucket:123/CANARY-S3", "s3://bucket/%2e%2e/CANARY-S3",
+  "s3://127.0.0.1/CANARY-S3", "s3://UPPERCASE/CANARY-S3",
 ];
 
 test.each(invalidS3Uris)("rejects invalid S3 URI %# without leaking it", (uri) => {
@@ -520,6 +523,7 @@ const invalidS3Endpoints = [
   { endpoint_url: "https://objects.example#CANARY-S3", trusted_endpoint: true },
   { endpoint_url: "https://objects.example", trusted_endpoint: false },
   { endpoint_url: "http://objects.example", trusted_endpoint: true, allow_insecure_endpoint: false },
+  { endpoint_url: "HTTP://objects.example", trusted_endpoint: true, allow_insecure_endpoint: false },
   { trusted_endpoint: true },
   { allow_private_endpoint: true },
   { allow_insecure_endpoint: true },