diff --git a/apps/meteor/app/authentication/server/lib/restrictLoginAttempts.ts b/apps/meteor/app/authentication/server/lib/restrictLoginAttempts.ts
index 300a4fa973114..1bf9c1dd6cbc6 100644
--- a/apps/meteor/app/authentication/server/lib/restrictLoginAttempts.ts
+++ b/apps/meteor/app/authentication/server/lib/restrictLoginAttempts.ts
@@ -2,6 +2,7 @@ import type { IServerEvent } from '@rocket.chat/core-typings';
 import { ServerEventType } from '@rocket.chat/core-typings';
 import { Logger } from '@rocket.chat/logger';
 import { Rooms, ServerEvents, Users } from '@rocket.chat/models';
+import { isIpInCidrRange } from '@rocket.chat/server-fetch';
 
 import { addMinutesToADate } from '../../../../lib/utils/addMinutesToADate';
 import { getClientAddress } from '../../../../server/lib/getClientAddress';
@@ -52,7 +53,15 @@ export const isValidLoginAttemptByIp = async (ip: string): Promise<boolean> => {
 	if (
 		!settings.get('Block_Multiple_Failed_Logins_Enabled') ||
 		!settings.get('Block_Multiple_Failed_Logins_By_Ip') ||
-		whitelist.includes(ip)
+		whitelist.some((entry) => {
+			const trimmed = entry.trim();
+			try {
+				return trimmed === ip || isIpInCidrRange(ip, trimmed);
+			} catch (error) {
+				logger.error({ msg: 'Invalid CIDR entry in whitelist', entry: trimmed, error });
+				return false;
+			}
+		})
 	) {
 		return true;
 	}
@@ -100,7 +109,9 @@ export const isValidAttemptByUser = async (login: ILoginAttempt): Promise<boolea
 		return true;
 	}
 
-	const loginUsername = login.methodArguments[0].user?.username;
+	const { username, email } = (login.methodArguments[0].user || {}) as { username?: string; email?: string };
+	const loginUsername = login.user?.username || username || email;
+
 	if (!loginUsername) {
 		return true;
 	}
@@ -147,7 +158,7 @@ export const isValidAttemptByUser = async (login: ILoginAttempt): Promise<boolea
 export const saveFailedLoginAttempts = async (login: ILoginAttempt): Promise<void> => {
 	const user: IServerEvent['u'] = {
 		_id: login.user?._id,
-		username: login.user?.username || login.methodArguments[0].user?.username,
+		username: login.user?.username || login.methodArguments[0].user?.username || login.methodArguments[0].user?.email,
 	};
 
 	await ServerEvents.insertOne({
@@ -161,7 +172,7 @@ export const saveFailedLoginAttempts = async (login: ILoginAttempt): Promise<voi
 export const saveSuccessfulLogin = async (login: ILoginAttempt): Promise<void> => {
 	const user: IServerEvent['u'] = {
 		_id: login.user?._id,
-		username: login.user?.username || login.methodArguments[0].user?.username,
+		username: login.user?.username || login.methodArguments[0].user?.username || login.methodArguments[0].user?.email,
 	};
 
 	await ServerEvents.insertOne({
diff --git a/apps/meteor/lib/utils/isRelativeURL.ts b/apps/meteor/lib/utils/isRelativeURL.ts
index aa682693df860..c289102206a29 100644
--- a/apps/meteor/lib/utils/isRelativeURL.ts
+++ b/apps/meteor/lib/utils/isRelativeURL.ts
@@ -1 +1,17 @@
-export const isRelativeURL = (str: string): boolean => /^[^\/]+\/[^\/].*$|^\/[^\/].*$/gim.test(str);
+export const isRelativeURL = (str: string): boolean => {
+	// Scheme-based URLs are absolute (e.g. https:, data:, javascript:).
+	if (/^[a-z][a-z\d+\-.]*:/i.test(str)) {
+		return false;
+	}
+
+	// URLs starting with // are protocol-relative, not path-relative.
+	if (str.startsWith('//')) {
+		return false;
+	}
+
+	if (str === '/' || str === '') {
+		return false;
+	}
+
+	return true;
+};
diff --git a/apps/meteor/tests/unit/lib/utils/isRelativeURL.spec.ts b/apps/meteor/tests/unit/lib/utils/isRelativeURL.spec.ts
index 86c054f0fcc11..d66dbb4a73a18 100644
--- a/apps/meteor/tests/unit/lib/utils/isRelativeURL.spec.ts
+++ b/apps/meteor/tests/unit/lib/utils/isRelativeURL.spec.ts
@@ -5,12 +5,16 @@ import { isRelativeURL } from '../../../../lib/utils/isRelativeURL';
 describe('isRelativeURL', () => {
 	const testCases = [
 		['/', false],
-		['test', false], // TODO: should be true?
+		['', false],
+		['test', true],
 		['test/test', true],
-		['.', false], // TODO: should be true?
+		['.', true],
 		['./test', true],
+		['../test', true],
+		['/test', true],
+		['//rocket.chat/path', false],
 		['https://rocket.chat', false],
-		['data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==', true], // TODO: should be false?
+		['data:image/gif;base64,R0lGODlhAQABAAAAACH5BAEKAAEALAAAAAABAAEAAAICTAEAOw==', false],
 	] as const;
 
 	testCases.forEach(([parameter, expectedResult]) => {
diff --git a/packages/server-fetch/src/helpers.ts b/packages/server-fetch/src/helpers.ts
index 69e10710f39aa..841f45c1efc14 100644
--- a/packages/server-fetch/src/helpers.ts
+++ b/packages/server-fetch/src/helpers.ts
@@ -50,7 +50,13 @@ export const isIpInCidrRange = (ip: string, cidr: string): boolean => {
 					groups.push(part);
 				}
 			}
-			return groups.reduce((value, hexGroup) => (value << 16n) + BigInt(parseInt(hexGroup, 16)), 0n);
+			return groups.reduce((value, hexGroup) => {
+				const parsed = parseInt(hexGroup, 16);
+				if (isNaN(parsed)) {
+					return value << 16n;
+				}
+				return (value << 16n) + BigInt(parsed);
+			}, 0n);
 		};
 		const mask = prefix === 0 ? 0n : ((1n << BigInt(prefix)) - 1n) << (128n - BigInt(prefix));
 		return (toBigInt(ip) & mask) === (toBigInt(network) & mask);
diff --git a/packages/server-fetch/src/index.ts b/packages/server-fetch/src/index.ts
index 2355d2a1b4754..4a693c6576fea 100644
--- a/packages/server-fetch/src/index.ts
+++ b/packages/server-fetch/src/index.ts
@@ -194,5 +194,6 @@ export async function serverFetch(input: string, options?: ExtendedFetchOptions,
 }
 
 export { Response };
+export { isIpInCidrRange } from './helpers';
 export type { ExtendedFetchOptions };
 export { parseSsrfAllowlist };
diff --git a/packages/server-fetch/tests/checkForSsrf.spec.ts b/packages/server-fetch/tests/checkForSsrf.spec.ts
index aceb4f69889c5..a08f442399214 100644
--- a/packages/server-fetch/tests/checkForSsrf.spec.ts
+++ b/packages/server-fetch/tests/checkForSsrf.spec.ts
@@ -297,9 +297,10 @@ describe('checkForSsrfHelpers', () => {
 				expect(isIpInCidrRange('::1', '127.0.0.0/8')).toBe(false);
 			});
 		});
-		it('returns false for invalid IP', () => {
+		it('returns false for malformed IP or CIDR', () => {
 			expect(isIpInCidrRange('not-an-ip', '192.168.0.0/16')).toBe(false);
 			expect(isIpInCidrRange('256.1.1.1', '192.168.0.0/16')).toBe(false);
+			expect(isIpInCidrRange('::1', '::g/128')).toBe(false); // Malformed hex group
 		});
 	});