Safari 18.x Fix — Mac Pro 4,1 / 5,1 with OCLP

Disclaimer — At Your Own Risk

This guide was developed through direct diagnostic work on a specific Mac Pro 4,1 (running 5,1 firmware) / 5,1 system, with assistance from Claude.ai (Anthropic). While the fix described here is confirmed working on that configuration, no guarantees can be made that results will be identical on every system. Any modifications made to your system — including EFI, kext, and LaunchDaemon changes — are made entirely at your own risk. This is not an official solution from Dortania or Apple, and has not undergone broad community testing. Always maintain a current backup before proceeding. Users are encouraged to share their results with the wider community to help validate and improve this fix.

Root Cause

Safari 18.2+ Requires AVX CPU Instructions Not Present on Mac Pro 4,1 / 5,1 Processors

Beginning with Safari 18.2, Apple's JavaScriptCore JIT compiler began emitting AVX (Advanced Vector Extensions) CPU instructions. Mac Pro 4,1 and 5,1 systems — including 4,1 models running the popular 5,1 firmware upgrade — are equipped with Intel Westmere-generation Xeon processors, which predate the Sandy Bridge architecture that introduced AVX support. When Safari's WebContent process attempts to execute JIT-compiled JavaScript, the CPU encounters an illegal instruction (SIGILL / EXC_BAD_INSTRUCTION), crashing the WebContent process repeatedly and producing the "a problem repeatedly occurred" error on every page load.

Firefox and other non-WebKit browsers are unaffected because they use independent JavaScript engines (SpiderMonkey, V8) that do not have this AVX dependency. The issue is strictly a CPU instruction incompatibility — it is not related to GPU, networking, or OCLP root patches.

Important Note Regarding OCLP 2.4.1

OCLP version 2.4.1 bundles RestrictEvents version 1.1.5, which does not include the JavaScriptCore patch required to resolve this issue. The fix was only committed to RestrictEvents in a post-release nightly build (version 1.1.7, March 19 2026 commit). Users must manually install this nightly build and add the appropriate boot argument — OCLP 2.4.1 does not handle this automatically.

Prerequisites & Before You Begin

Before Starting

Use Firefox or Brave to download files during this procedure — Safari is not functional. Ensure you have administrator access to your Mac. A recent Time Machine backup is strongly recommended before making any EFI changes.

This guide applies to Mac Pro 4,1 and 5,1 systems — including 4,1 models that have been upgraded to 5,1 firmware, which is a common and widely-used modification that makes the two models functionally identical for the purposes of this fix. The guide assumes your system is running macOS Ventura via OCLP 2.4.1 with Safari 18.x installed and failing to load web pages.

The fix requires two components working together:

① RestrictEvents 1.1.7 nightly — patches JavaScriptCore at the kernel level to handle pre-AVX CPUs
② JIT Disable LaunchDaemon — provides a second layer of protection by disabling JIT compilation at the process level

Updating Safari to 18.x on Ventura

Safari 18.x can be installed via System Preferences → Software Update, or via a trusted standalone installer from Apple or reputable Mac community resources. Either method produces the same result. Note that standalone installers update the Safari app bundle but rely on the system's existing WebKit frameworks — always re-run OCLP Post-Install Root Patches after any Safari or macOS update.

Install RestrictEvents 1.1.7

Download the RestrictEvents 1.1.7 nightly build

In Firefox or Brave, navigate to the RestrictEvents GitHub Actions page. A free GitHub account login is required to download artifacts.

https://github.com/acidanthera/RestrictEvents/actions

Find the workflow run titled "Add JavaScriptCore patches for pre-AVX CPUs" (dated March 19, 2026) with a green checkmark. Click it, scroll to the Artifacts section at the bottom, and download the RELEASE zip (not DEBUG). Extract it to get RestrictEvents.kext.

Alternative Download

If you do not have a GitHub account, try the Dortania builds mirror:
https://dortania.github.io/builds/?product=RestrictEvents&viewall=true
Download the most recent build dated after July 2025.

Mount your EFI partition

Open Terminal and run:

sudo diskutil mount disk0s1

Your EFI partition will mount at /Volumes/EFI. If your boot drive is not disk0, use diskutil list to identify the correct identifier first.

Replace the existing RestrictEvents kext

Run these commands in Terminal:

sudo rm -rf /Volumes/EFI/EFI/OC/Kexts/RestrictEvents.kext
sudo cp -r ~/Downloads/RestrictEvents.kext /Volumes/EFI/EFI/OC/Kexts/

Verify the correct version is in place

defaults read /Volumes/EFI/EFI/OC/Kexts/RestrictEvents.kext/Contents/Info.plist CFBundleVersion

Should return 1.1.7. If it returns anything else, the correct file was not copied — repeat step 3.

Edit config.plist Boot Arguments

Open config.plist in TextEdit

In Finder, press Cmd+Shift+G and navigate to:

/Volumes/EFI/EFI/OC/

Right-click config.plist → Open With → TextEdit. Immediately switch to plain text mode via Format → Make Plain Text.

Find the boot-args entry

Press Cmd+F and search for boot-args. Locate the <string>...</string> line holding your boot arguments. A default OCLP 2.4.1 installation does not include any revpatch entry — your string will look similar to:

keepsyms=1 debug=0x100 -lilubetaall -btlfxallowanyaddr ipc_control_port_options=0 -nokcmismatchpanic

The exact arguments in your string may differ — that is normal.

Add revpatch=sbvmm,jsc to your boot-args

Append revpatch=sbvmm,jsc to the end of your existing boot-args string, separated from the last argument by a single space. The sbvmm value is required by OCLP for macOS virtualisation compatibility, and jsc explicitly activates the JavaScriptCore patch in RestrictEvents. Your string should end up looking similar to:

keepsyms=1 debug=0x100 -lilubetaall -btlfxallowanyaddr ipc_control_port_options=0 -nokcmismatchpanic revpatch=sbvmm,jsc

Critical

Do not remove or alter any existing arguments in your boot-args string — only add revpatch=sbvmm,jsc to the end. If your boot-args already contain an existing revpatch entry such as revpatch=auto or revpatch=sbvmm, replace that existing entry with revpatch=sbvmm,jsc rather than adding a second one. Two revpatch entries will cause conflicts.

Save and unmount

Press Cmd+S to save, close TextEdit, then unmount the EFI partition:

sudo diskutil unmount disk0s1

Install the JIT Disable LaunchDaemon

Create the plist file in TextEdit

Open TextEdit, switch to plain text mode (Format → Make Plain Text), and paste the following content exactly:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN"
  "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
  <key>Label</key>
  <string>com.user.jsc-nojit</string>
  <key>ProgramArguments</key>
  <array>
    <string>/bin/sh</string>
    <string>-c</string>
    <string>launchctl setenv JSC_useJIT false; launchctl setenv __XPC_JSC_useJIT false</string>
  </array>
  <key>RunAtLoad</key>
  <true/>
</dict>
</plist>

Save to Desktop

Press Cmd+Shift+S to Save As. Name the file exactly:

com.user.jsc-nojit.plist

Save it to your Desktop in Plain Text format (not Rich Text).

Install and activate

Run this single Terminal command to move the file to the correct system location, set the correct permissions, and activate it immediately:

sudo cp ~/Desktop/com.user.jsc-nojit.plist /Library/LaunchDaemons/ && sudo chmod 644 /Library/LaunchDaemons/com.user.jsc-nojit.plist && sudo chown root:wheel /Library/LaunchDaemons/com.user.jsc-nojit.plist && sudo launchctl load /Library/LaunchDaemons/com.user.jsc-nojit.plist

Reboot and Verify

Reboot your Mac

Reboot normally. Let the system finish loading completely before opening Safari.

Confirm RestrictEvents 1.1.7 is loaded

kextstat | grep -i restrict

Output should show (1.1.7) in the version field.

Confirm JIT disable is active

launchctl getenv JSC_useJIT

Should return false.

Test Safari

Open Safari and attempt to load a web page. Pages should now load normally without the "a problem repeatedly occurred" error.

✓ Expected Result

Safari 18.x loads web pages successfully. JavaScript executes without crashing. No new WebContent crash reports appear in ~/Library/Logs/DiagnosticReports/ after browsing.

Reversing the JIT Disable (If Needed)

If a future OCLP or RestrictEvents update fully resolves the issue without the JIT disable workaround, remove it with these two commands, then reboot:

sudo launchctl unload /Library/LaunchDaemons/com.user.jsc-nojit.plist
sudo rm /Library/LaunchDaemons/com.user.jsc-nojit.plist

The RestrictEvents kext and revpatch boot argument can remain in place — they are beneficial regardless.

Possible Pitfalls

Wrong RestrictEvents version installed Versions 1.1.5 and 1.1.6 do not contain the JSC patch. Always verify the installed version after copying. The correct build is specifically the March 19 2026 GitHub Actions artifact titled "Add JavaScriptCore patches for pre-AVX CPUs."
Duplicate revpatch entry in boot-args If your boot-args already contain a revpatch entry (such as revpatch=auto or revpatch=sbvmm), do not add a second one — replace the existing entry with revpatch=sbvmm,jsc. Two revpatch entries will cause conflicts and may prevent the JSC patch from activating correctly.
Safari and WebKit version mismatch A Safari standalone .pkg installer updates the Safari app bundle but not the system WebKit frameworks, which are only updated via full macOS point releases. If Safari is significantly ahead of the system WebKit version, additional instability may occur even after applying this fix.
OCLP root patches not re-run after a Safari or macOS update Any macOS or Safari update may overwrite system components that OCLP has patched. Always re-run OCLP Post-Install Root Patches immediately after any system update, before opening Safari or other patched applications.
GitHub login required for nightly artifact download GitHub requires a free account login to download Actions artifacts. If this is not possible, use the Dortania builds mirror as an alternative source.
TextEdit saving in Rich Text format If TextEdit is not switched to Plain Text mode before saving the LaunchDaemon plist, it will save as .rtf with formatting markup, rendering the file invalid. Always verify Format → Make Plain Text before pasting or saving.

Recommendations for the OCLP Development Team

The following improvements would prevent this class of issue from affecting Mac Pro 4,1 / 5,1 users — including 4,1 systems running 5,1 firmware — in future OCLP releases, bringing the Safari 18.x fix within the standard OCLP patching workflow without requiring manual intervention.

Bundle RestrictEvents 1.1.7 or later in future OCLP releases The JavaScriptCore patch for pre-AVX CPUs is committed to RestrictEvents master as of March 19 2026. The next OCLP release should bundle this version at minimum, replacing the currently included 1.1.5. This is the single most impactful change and would resolve the issue for most affected Mac Pro 4,1 / 5,1 users automatically.
Automatically set revpatch=sbvmm,jsc for pre-AVX hardware during EFI build OCLP already detects the Mac Pro 4,1 / 5,1 hardware class and knows it lacks AVX support via hardware probing. The EFI build process should automatically include jsc in the revpatch boot argument for these machines, rather than relying on users to add it manually.
Add a pre-AVX CPU detection check during post-install root patching During the root patch process, OCLP could detect the absence of AVX CPU flags and automatically install the JIT disable LaunchDaemon as part of the patch set — similar to how it already installs other compatibility plists. This would make the fix entirely automatic for affected Mac Pro 4,1 / 5,1 hardware.
Add a compatibility warning when Safari 18.2+ is detected on pre-AVX hardware OCLP's post-install patcher could check the installed Safari version against CPU capabilities and alert the user if a known-incompatible version is detected, with guidance on applying the fix. This would surface the issue immediately on any Mac Pro 4,1 / 5,1 system, rather than leaving users to discover it through unexplained browser failure.
Document the Safari 18.x / AVX incompatibility in release notes Until an automatic fix is in place, the OCLP changelog and documentation for releases targeting Mac Pro 4,1 / 5,1 systems should explicitly note the Safari 18.2+ AVX incompatibility and link to a manual fix procedure, preventing users from spending significant time diagnosing an already-understood issue.

Community Note

This guide was researched and authored by ptrix, March 2026, with diagnostic assistance from Claude.ai (Anthropic). The fix is confirmed working on a Mac Pro 4,1 (running 5,1 firmware) / 5,1 system running macOS Ventura 13.7.8 via OCLP 2.4.1. Community members who verify this fix on Mac Pro 4,1 / 5,1 systems — both native 5,1 hardware and 4,1 systems running the 5,1 firmware upgrade — are encouraged to submit their results to the OCLP GitHub issue tracker at https://github.com/dortania/OpenCore-Legacy-Patcher/issues to help the development team prioritize an official solution. Wider community testing and collaboration are welcomed and needed.