libcurl versions from 7.36.0 to before 7.64.0 are vulnerable to a stack-based buffer overflow. The function creating an outgoing NTLM type-3 header (lib/vauth/ntlm.c:Curl_auth_create_ntlm_type3_message()), generates the request HTTP header contents based on previously received data. The check that exists to prevent the local buffer from getting overflowed is implemented wrongly (using unsigned math) and as such it does not prevent the overflow from happening. This output data can grow larger than the local buffer if very large nt response data is extracted from a previous NTLMv2 header provided by the malicious or broken HTTP server. Such a large value needs to be around 1000 bytes or more. The actual payload data copied to the target buffer comes from the NTLMv2 type-2 response header.
Weakness
A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).
Affected Software
| Name |
Vendor |
Start Version |
End Version |
| Libcurl |
Haxx |
7.36.0 (including) |
7.64.0 (excluding) |
| JBoss Core Services Apache HTTP Server 2.4.29 SP2 |
RedHat |
|
* |
| Red Hat Enterprise Linux 8 |
RedHat |
curl-0:7.61.1-11.el8 |
* |
| Curl |
Ubuntu |
bionic |
* |
| Curl |
Ubuntu |
cosmic |
* |
| Curl |
Ubuntu |
devel |
* |
| Curl |
Ubuntu |
upstream |
* |
| Curl |
Ubuntu |
xenial |
* |
Potential Mitigations
- Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking.
- D3-SFCV (Stack Frame Canary Validation) from D3FEND [REF-1334] discusses canary-based detection in detail.
- Run or compile the software using features or extensions that randomly arrange the positions of a program’s executable and libraries in memory. Because this makes the addresses unpredictable, it can prevent an attacker from reliably jumping to exploitable code.
- Examples include Address Space Layout Randomization (ASLR) [REF-58] [REF-60] and Position-Independent Executables (PIE) [REF-64]. Imported modules may be similarly realigned if their default memory addresses conflict with other modules, in a process known as “rebasing” (for Windows) and “prelinking” (for Linux) [REF-1332] using randomly generated addresses. ASLR for libraries cannot be used in conjunction with prelink since it would require relocating the libraries at run-time, defeating the whole purpose of prelinking.
- For more information on these techniques see D3-SAOR (Segment Address Offset Randomization) from D3FEND [REF-1335].
References