diff --git a/packages/core/src/install.js b/packages/core/src/install.js
index d5f3ff391..9cda71013 100644
--- a/packages/core/src/install.js
+++ b/packages/core/src/install.js
@@ -139,6 +139,29 @@ export async function download({
   return exec;
 }
 
+const DEFAULT_CHROMIUM_BASE_URL = 'https://storage.googleapis.com/chromium-browser-snapshots/';
+
+// Resolve the Chromium download base URL. PERCY_CHROMIUM_BASE_URL may point at a
+// private mirror, but an unvalidated value enables SSRF / an integrity downgrade
+// (CWE-918): require a well-formed HTTPS URL, otherwise warn and fall back to the
+// trusted default host.
+export function resolveChromiumBaseUrl(value = process.env.PERCY_CHROMIUM_BASE_URL) {
+  if (!value) return DEFAULT_CHROMIUM_BASE_URL;
+  let log = logger('core:install');
+  let parsed;
+  try {
+    parsed = new URL(value);
+  } catch {
+    log.warn(`Invalid PERCY_CHROMIUM_BASE_URL "${value}"; using the default Chromium download host.`);
+    return DEFAULT_CHROMIUM_BASE_URL;
+  }
+  if (parsed.protocol !== 'https:') {
+    log.warn(`Ignoring non-HTTPS PERCY_CHROMIUM_BASE_URL "${value}"; Chromium must be downloaded over HTTPS.`);
+    return DEFAULT_CHROMIUM_BASE_URL;
+  }
+  return value.endsWith('/') ? value : `${value}/`;
+}
+
 // Installs a revision of Chromium to a local directory
 export function chromium({
   // default directory is within @percy/core package root
@@ -148,7 +171,7 @@ export function chromium({
 } = {}) {
   let extract = (i, o) => import('extract-zip').then(ex => ex.default(i, { dir: o }));
 
-  let url = (process.env.PERCY_CHROMIUM_BASE_URL || 'https://storage.googleapis.com/chromium-browser-snapshots/') +
+  let url = resolveChromiumBaseUrl() +
     selectByPlatform({
       linux: `Linux_x64/${revision}/chrome-linux.zip`,
       darwin: `Mac/${revision}/chrome-mac.zip`,
diff --git a/packages/core/src/percy.js b/packages/core/src/percy.js
index 2878299c5..1fa50f267 100644
--- a/packages/core/src/percy.js
+++ b/packages/core/src/percy.js
@@ -863,7 +863,10 @@ export class Percy {
     if (!process.env.PERCY_TOKEN) return;
     try {
       const logsObject = {
-        clilogs: logger.query(log => !['ci'].includes(log.debug))
+        // Redact secrets from CLI logs before egress to the Percy API — these
+        // can contain tokens or URLs with embedded credentials (CWE-532). The
+        // cilogs below were already redacted; clilogs were not.
+        clilogs: redactSecrets(logger.query(log => !['ci'].includes(log.debug)))
       };
 
       // Only add CI logs if not disabled voluntarily.
diff --git a/packages/core/src/snapshot.js b/packages/core/src/snapshot.js
index 8d23e9352..703f86ab5 100644
--- a/packages/core/src/snapshot.js
+++ b/packages/core/src/snapshot.js
@@ -45,21 +45,31 @@ function validateAndFixSnapshotUrl(snapshot) {
 // used to deserialize regular expression strings
 const RE_REGEXP = /^\/(.+)\/(\w+)?$/;
 
+// Upper bound on the snapshot name length we will run user-controllable
+// regex/glob matching against. A crafted, very long snapshot name reaching this
+// matcher (e.g. via the local API) combined with a backtracking-prone pattern
+// could otherwise trigger catastrophic backtracking / ReDoS (CWE-1333). Real
+// snapshot names are short; an over-long name simply does not match patterns.
+const MAX_MATCH_INPUT_LENGTH = 2048;
+
 // Returns true or false if a snapshot matches the provided include and exclude predicates. A
 // predicate can be an array of predicates, a regular expression, a glob pattern, or a function.
 function snapshotMatches(snapshot, include, exclude) {
   // support an options object as the second argument
   if (include?.include || include?.exclude) ({ include, exclude } = include);
 
+  // guard pattern matching against pathologically long inputs (ReDoS)
+  let patternSafe = typeof snapshot.name === 'string' && snapshot.name.length <= MAX_MATCH_INPUT_LENGTH;
+
   // recursive predicate test function
   let test = (predicate, fallback) => {
     if (predicate && typeof predicate === 'string') {
-      // snapshot name matches exactly or matches a glob
+      // exact match is always safe; glob matching is only run on bounded input
       let result = snapshot.name === predicate ||
-        micromatch.isMatch(snapshot.name, predicate);
+        (patternSafe && micromatch.isMatch(snapshot.name, predicate));
 
-      // snapshot might match a string-based regexp pattern
-      if (!result) {
+      // snapshot might match a string-based regexp pattern (bounded input only)
+      if (!result && patternSafe) {
         try {
           let [, parsed, flags] = RE_REGEXP.exec(predicate) || [];
           result = !!parsed && new RegExp(parsed, flags).test(snapshot.name);
@@ -68,8 +78,8 @@ function snapshotMatches(snapshot, include, exclude) {
 
       return result;
     } else if (predicate instanceof RegExp) {
-      // snapshot matches a regular expression
-      return predicate.test(snapshot.name);
+      // snapshot matches a regular expression (bounded input only)
+      return patternSafe && predicate.test(snapshot.name);
     } else if (typeof predicate === 'function') {
       // advanced matching
       return predicate(snapshot);
diff --git a/packages/core/src/utils.js b/packages/core/src/utils.js
index dee1dea6f..5b683d3c4 100644
--- a/packages/core/src/utils.js
+++ b/packages/core/src/utils.js
@@ -553,10 +553,23 @@ export async function withRetries(fn, { count, onRetry, signal, throwOn }) {
   }
 }
 
-export function redactSecrets(data) {
-  const filepath = path.resolve(url.fileURLToPath(import.meta.url), '../secretPatterns.yml');
-  const secretPatterns = YAML.parse(readFileSync(filepath, 'utf-8'));
+// Lazily load and compile the secret patterns once. The pattern file holds
+// ~1.7k regexes; parsing the YAML and compiling every RegExp on each call made
+// redactSecrets O(patterns) per string and re-read the file for every recursive
+// call. Since redactSecrets now runs over the full CLI log array on egress
+// (sendBuildLogs), that per-call cost is paid hundreds of times and could blow
+// past test/runtime timeouts. Compile once and reuse.
+let _compiledSecretPatterns;
+function getSecretPatterns() {
+  if (!_compiledSecretPatterns) {
+    const filepath = path.resolve(url.fileURLToPath(import.meta.url), '../secretPatterns.yml');
+    const secretPatterns = YAML.parse(readFileSync(filepath, 'utf-8'));
+    _compiledSecretPatterns = secretPatterns.patterns.map(p => new RegExp(p.pattern.regex, 'g'));
+  }
+  return _compiledSecretPatterns;
+}
 
+export function redactSecrets(data) {
   if (Array.isArray(data)) {
     // Process each item in the array
     return data.map(item => redactSecrets(item));
@@ -565,8 +578,8 @@ export function redactSecrets(data) {
     data.message = redactSecrets(data.message);
   }
   if (typeof data === 'string') {
-    for (const pattern of secretPatterns.patterns) {
-      data = data.replace(new RegExp(pattern.pattern.regex, 'g'), '[REDACTED]');
+    for (const pattern of getSecretPatterns()) {
+      data = data.replace(pattern, '[REDACTED]');
     }
   }
   return data;
diff --git a/packages/core/test/unit/install.test.js b/packages/core/test/unit/install.test.js
index d27f15f0e..6c7fe0a84 100644
--- a/packages/core/test/unit/install.test.js
+++ b/packages/core/test/unit/install.test.js
@@ -291,6 +291,46 @@ describe('Unit / Install', () => {
       });
     }
   });
+
+  describe('resolveChromiumBaseUrl', () => {
+    let defaultUrl = 'https://storage.googleapis.com/chromium-browser-snapshots/';
+
+    afterEach(() => {
+      delete process.env.PERCY_CHROMIUM_BASE_URL;
+    });
+
+    it('returns the default host when no base URL is set', () => {
+      delete process.env.PERCY_CHROMIUM_BASE_URL;
+      expect(install.resolveChromiumBaseUrl()).toEqual(defaultUrl);
+    });
+
+    it('reads the base URL from PERCY_CHROMIUM_BASE_URL by default', () => {
+      process.env.PERCY_CHROMIUM_BASE_URL = 'https://mirror.test.com/';
+      expect(install.resolveChromiumBaseUrl()).toEqual('https://mirror.test.com/');
+    });
+
+    it('appends a trailing slash to a valid HTTPS base URL', () => {
+      expect(install.resolveChromiumBaseUrl('https://mirror.test.com/chromium'))
+        .toEqual('https://mirror.test.com/chromium/');
+    });
+
+    it('leaves an already slash-terminated base URL unchanged', () => {
+      expect(install.resolveChromiumBaseUrl('https://mirror.test.com/'))
+        .toEqual('https://mirror.test.com/');
+    });
+
+    it('falls back to the default host for an unparseable URL', () => {
+      expect(install.resolveChromiumBaseUrl('not a valid url')).toEqual(defaultUrl);
+      expect(logger.stderr).toContain(
+        '[percy] Invalid PERCY_CHROMIUM_BASE_URL "not a valid url"; using the default Chromium download host.');
+    });
+
+    it('rejects a non-HTTPS base URL and falls back to the default host', () => {
+      expect(install.resolveChromiumBaseUrl('http://mirror.test.com/')).toEqual(defaultUrl);
+      expect(logger.stderr).toContain(
+        '[percy] Ignoring non-HTTPS PERCY_CHROMIUM_BASE_URL "http://mirror.test.com/"; Chromium must be downloaded over HTTPS.');
+    });
+  });
 });
 
 describe('Unit / Install in executable', () => {