Apple Web Content Filter Bypass

Dear colleagues,Nosebeard Labs is pleased to share its latest advisory, detailing a bypass of Apple's system wide web content filter. The HTML version of this advisory is also available at:https://nosebeard.co/advisories/nbl-001.htmlWarmest regards,Nosebeard Labs## SummaryNosebeard Labs Security Advisory NBL-001Title: Apple web content filter bypass allows unrestricted access to blocked content (macOS/iOS/iPadOS/visionOS/watchOS)Advisory ID: NBL-001Date: 2024-11-15Severity: Critical (CVSS 9.1)Affected Product: Safari on any Apple device with Screen Time enabledCVE ID: CVE-2024-44206## OverviewNosebeard Labs has identified a critical vulnerability in Apple’s system wide web content filter that allows a full bypass of content restrictions. This vulnerability, which occurs specifically when Screen Time’s content filtering settings are enabled, permits users or attackers to access restricted websites in Safari without detection. By exploiting a misalignment between Screen Time’s Access Control List (ACL) and WebKit’s URI validation, a specially crafted URI can circumvent both layers of protection.Apple has assigned CVE-2024-44206 to this issue and issued a fix for macOS Sonoma 14.x, iOS/iPadOS 17.x, watchOS 10.x, visionOS 1.x, Safari 17.x and up.However, a fix is still pending for the backport channels.## DescriptionThis vulnerability arises when the WebKit Cocoa layer in Safari ingests a URI without performing comprehensive validation, combined with a failure by the Screen Time ACL filter to recognize and block the malformed URI. The flaw allows a crafted URI to bypass all Screen Time content filtering settings, including deny/allow lists and parental content filters, providing unrestricted access to blocked content.## Affected SystemsThis vulnerability affects all devices on macOS, iOS, iPadOS, watchOS and visionOS platforms with Safari and Screen Time enabled, impacting an estimated 250 million devices globally.## Attack ScenariosThe vulnerability can be exploited both locally and remotely:1. Local Exploitation: Users can manipulate the address bar to manually enter a crafted URI, bypassing Screen Time restrictions.2. Network-Based Exploitation: Attackers can load restricted content remotely by embedding a crafted URI within an iframe, bypassing restrictions without requiring user interaction.## Impact1. Confidentiality: Unrestricted access to restricted websites compromises the confidentiality of content filtering controls, potentially exposing sensitive or inappropriate material.2. Scope and Integrity: This vulnerability spans across two separate security mechanisms (Screen Time and WebKit), representing a critical architecture-level issue. Additionally, accessing unsecured or unlogged resources poses potential integrity risks.## CVSS ScoreVector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:H/I:L/A:NScore: 9.1 (Critical)## MitigationsUpgrade to the latest iOS/iPadOS 17.x or 18.x / macOS Sonoma 14.x  / visionOS 1.x / watchOS 10.x / Safari 17.6 respectively. Users who are unable to apply a fix can contact us for more info.## Vendor ResponseApple has issued CVE-2024-44206 and supplied a fix within WebKit; however, a fix remains pending for iOS/iPadOS version 16.x. We recommend that Apple undertake further review to address the issue comprehensively.## Timeline–Milestone:2020-11-24 Vulnerability discovered internally at NBL–Milestone:2021-03-08 Initial disclosure to Apple Product Security–2021-03-09 Apple Product Security recommends to open a bug report on Feedback Assistant2021-03-10 We opened a bug report on Feedback Assistant as advised by Apple Product Security2021-03-15 We follow-up by adding additional info to the open bug report on F.A.2021-08-16 We follow-up again referring Apple Product Security to open ticket, stressing that the issue can be also demonstrated in their EU Apple Stores2021-08-24 We follow-up again to Apple Product Security, referring to the previous follow-up2021-08-25 Rejected by Apple Security - “We do not see any actual security implications. We recommended reporting this issue via Feedback Assistant”2024-03-18 NBL submits a second report 3 years later to appeal via Apple Security Bounty Program, urging to re-evaluate, also providing PoC code2024-03-19 Apple Security Research closes report - “We’re unable to identify a security issue in your report” - “Screen Time is not intended to protect a device against manipulation” - “We recommend reporting this via Feedback Assistant”2024-04-02 Status of Bug Report on F.A. from 2021-03-10 “Open, Similar Reports None”2024-04-03 We follow-up again asking Apple Security for a final reassessment, providing a temporary workaround2024-04-03 Apple Security recommends opening a bug report - “ST is not intended to protect a device against manipulation” - “MDM profiles provide configuration management but do not establish additional security boundaries beyond what iOS and iPadOS have to offer.”2024-05-05 Initial contact with Joanna Stern of WSJ2024-05-06 Referring PSIRT ticket # directly to an Apple PSIRT contact via undisclosed SOC - no response2024-05-28 Joanna Stern/WSJ runs Apple through this2024-05-29 Apple commits patches to Safari branch–Milestone:2024-06-05 Wall Street Journal addresses our finding in their article “A Bug Allowed Kids to Visit X-Rated Sites. Apple Took Three Years to Fix It.” by Joanna Stern–2024-06-18 We follow-up again with Urgent request for re-evaluation to Apple Product Security (“Addendum”)2024-06-27 We follow-up on our follow-up Update Request Screen Time Security Vulnerability Report (“Follow-Up”)2024-07-23 Apple releases fix in iOS 17.6RC et al.2024-07-26 Letter to Apple welcoming first fix, reiterating our dedication to Responsible Disclosure, intended to coordinate further disclosure process and close the affair asking them to give credit and align to their SBP–Milestone:2024-07-29 Apple releases fixes for macOS Sonoma 14.6, iOS/iPadOS 17.6, watchOS 10.6, visionOS 1.3 and Safari 17.6, leaving iOS/iPadOS 16.x still affected.–2024-07-31 Apple responds “ST is not intended to protect a device from malicious manipulation, and bug reports on features like this are therefore typically ineligible for credit or Apple Security Bounty award. However, we’d like to make an exception and award you USD (...)* as a thank you for your report. Also, we’d like to credit you on our security advisory under the ‘Additional recognition’ section of the page.” *We were offered the minimum possible amount.2024-08-01 We inquire about the bounty amount asking Apple to “comment on our proposed evaluation under the CVSS metrics, sharing with us their transparent assessment of the vulnerability under the terms and broad criteria of the bounty program.”2024-08-01 Apple “appreciates our suggestions, but CVSS scores are not something that they publish to their security advisory.”2024-08-03 Patches merged with public WebKit branch2024-08-19 We are reaching out to Apple again “Ringing the escalation bell for the SBP team”2024-08-23 Apple Product Security advises a call2024-09-10 Apple Security rejects adjustment of the bounty as “out of scope/edge case policy” in the call, offering a $20,000 charity donation instead We request Apple to assign a CVE.–Milestone:2024-10-17 Apple follows-up with CVE-2024-44206 and an update to the advisorieshttps://support.apple.com/en-us/120909https://support.apple.com/en-us/120911https://support.apple.com/en-us/120913https://support.apple.com/en-us/120915https://support.apple.com/en-us/120916–2024-10-23 We follow-up one more time to request a further review of the severity and reward2024-11-02 NBL-001 advisory draft shared with Apple2024-11-14 Apple requests naming their charity offer among bounty payout details, leaving out further comments on the contents of the advisory itself.2024-11-15 NBL-001 published## ContactFor more information, please contact Andreas Jaegersberger or Ro Achterberg from Nosebeard Labs at [email protected].## Special ThanksMuch love goes out to Joanna Stern for her incredible support in making this happen.We also want to thank Aaron Kaplan for the tailwind throughout the journey and Arnoud Engelfriet for the rapid legal advice.Buongiorno to the cap’n <3