Deep technical analysis of heap corruption vulnerability in Internet Communication Manager
SAP Web Dispatcher and Internet Communication Manager (ICM) contain a critical memory corruption vulnerability in the HTTP header parsing function. The vulnerability allows an unauthenticated attacker to cause heap corruption and lead to Denial of Service through specially crafted HTTP requests.
Executive Summary
During analysis of SAP Security Note 3677544, we conducted deep binary analysis of SAP Web Dispatcher patch level 1526 (vulnerable) and 1528 (patched). The research revealed the exact nature of the vulnerability and its exploitation mechanism.
🔴 CVE-2025-42877 CVSS 7.5
Memory Corruption in IctHttpOpenMessage - Insufficient error handling during memory allocation for HTTP headers leads to heap corruption. The vulnerable code continues execution with an invalid pointer after allocation failure, causing ICM/Web Dispatcher crash.
Location: sapwebdisp binary, function IctHttpOpenMessage at 0x3919a0
Impact: Denial of Service (High Availability Impact), No Confidentiality/Integrity Impact
Technical Nature of the Vulnerability
► Heap Corruption Mechanism
The vulnerability resides in the IctHttpOpenMessage function, which processes incoming HTTP requests. When parsing each HTTP header, the function calls IctIHttpAddMemoryExtension to allocate 12 bytes of memory.
The problem occurs when:
- ICM/Web Dispatcher heap memory is fragmented by multiple requests
- An HTTP request arrives with a large number of headers (200-500 count)
- For one of the headers,
IctIHttpAddMemoryExtension(12)fails to allocate memory - The vulnerable code makes only 1 retry attempt, then CONTINUES EXECUTION
- Code attempts to write data to invalid pointer → heap corruption → crash
❌ Vulnerable Code (PL 1526)
✅ Patched Code (PL 1528)
Exploitation: Trigger HTTP Request
To exploit the vulnerability, a series of HTTP requests must be sent with gradually increasing number of headers. This is NOT one huge request, but a sequence of 40+ requests.
Each HTTP header in the request triggers internal SAP parsing, which requires allocation of 12 bytes of memory through IctIHttpAddMemoryExtension().
A request with 350 headers = 350 potential allocations of 12 bytes each. After preliminary heap memory fragmentation (Phase 1), one of these allocations fails.
The vulnerable version performs only 1 retry, which also fails, and then continues using the invalid buffer → heap corruption → ICM crash.
► Exploit Request Structure
Phase 1: Memory Fragmentation (8 seconds)
Send 300+ requests with 100 headers each to fragment ICM heap memory
Phase 2: Trigger (40 requests)
Gradually increase header count: Request 1 → 200 headers, Request 20 → 350 headers, Request 40 → 500 headers
Will be available after 90 days from SAP Security Patch Day.
Key Request Parameters
| Number of headers | 200-500 count (gradual increase) |
| Size of each header | ~200 bytes (name + value) |
| Cookie header | 50 values × 100 bytes = ~5 KB |
| Total header size | ~70-100 KB (for 350 headers) |
| SOAP body | Minimal (~200 bytes, not critical) |
| Target endpoint | /sap/bc/soap/rfc?sap-client=001 |
► Attack Sequence
30 threads × 10 requests = 300 requests with 100 headers each
ICM/Web Dispatcher allocates many small memory blocks (12 bytes × 100 headers × 300 requests). Heap becomes fragmented, free memory scattered in small chunks.
Gradual increase: 200 → 350 → 500 headers
Each request triggers 200-500 calls to IctIHttpAddMemoryExtension(12). Due to fragmentation, one of the allocations fails. Vulnerable version makes 1 retry (also fails) and CONTINUES with invalid buffer.
Write to invalid pointer
Code attempts to write header data to invalid pointer → heap metadata corruption → adjacent heap chunks corrupted → next malloc/free operation triggers CRASH → ICM/Web Dispatcher terminates → Denial of Service.
Binary Analysis Results
We conducted detailed binary analysis of both SAP Web Dispatcher versions:
Version Comparison
| Parameter | Vulnerable (PL 1526) | Patched (PL 1528) |
|---|---|---|
| Function address | 0x3919a0 |
0x3914b0 |
| Function size | 0x1f7a (8,058 bytes) | 0x20ba (8,378 bytes) |
| Size change | +320 bytes (+3.97%) | |
| Retry attempts | 1 attempt | 3+ attempts with loop |
| Bounds validation | ❌ None | ✅ After each attempt |
| Failure handling | ❌ Continue anyway | ✅ Keep retrying |
Protection and Mitigation
If you are using SAP Web Dispatcher or SAP NetWeaver with patch level < 1528, apply the patch immediately. This is not a theoretical vulnerability — it has been confirmed through binary analysis and can be exploited in production environments.
Immediate Actions
- Apply SAP Note 3677544 — update kernel to PL 1528 or higher
- Restart ICM/Web Dispatcher after applying the patch
- Review logs for the last 30 days for signs of exploitation
- Monitor for unusual crashes or memory errors
Impact Assessment
CVSS 3.1 Vector
| Attack Vector: | Network |
| Attack Complexity: | Low |
| Privileges Required: | None |
| User Interaction: | None |
| Availability Impact: | High |
Conclusion
CVE-2025-42877 represents a critical heap corruption vulnerability in SAP Web Dispatcher and ICM, caused by insufficient error handling during memory allocation for HTTP headers.
Our binary analysis revealed that the vulnerability arises because the IctHttpOpenMessage function makes only one retry attempt for memory allocation upon failure, after which it continues execution with an invalid pointer. This leads to heap corruption and ICM/Web Dispatcher crash.
Exploiting the vulnerability requires sending a series of HTTP requests with gradually increasing number of headers (200-500), which under conditions of fragmented heap memory leads to allocation failures and subsequent crash.
Organizations using SAP Web Dispatcher or SAP NetWeaver must immediately apply SAP Security Note 3677544 and update kernel to patch level 1528 or higher. The vulnerability has been confirmed through source code analysis and can be exploited in production environments.
Analysis by: Security Research Team
Publication Date: January 2026
CVE: CVE-2025-42877
SAP Security Note: 3677544
Affected: SAP Web Dispatcher PL < 1528, ICM in SAP NetWeaver, SAP Content Server
