CVE-2023-27882
A heap-based buffer overflow vulnerability exists in the HTTP Server form boundary functionality of Weston Embedded uC-HTTP v3.01.01. A specially crafted network packet can lead to code execution. An attacker can send a malicious packet to trigger this vulnerability.
The versions below were either tested or verified to be vulnerable by Talos or confirmed to be vulnerable by the vendor.
Weston Embedded uC-HTTP v3.01.01
Weston Embedded Cesium NET 3.07.01
Silicon Labs Gecko Platform 4.3.1.0
uC-HTTP - https://weston-embedded.com/micrium/overview Cesium NET - https://www.weston-embedded.com/cesium-cs-net Gecko Platform - https://www.silabs.com/developers/gecko-software-development-kit
9.0 - CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
CWE-122 - Heap-based Buffer Overflow
The uC-HTTP server implementation is designed to be used on embedded systems that are running the µC/OS II or µC/OS III RTOS kernels. This HTTP server supports many features including persistent connections, form processing, chunked transfer encoding, HTTP header fields processing, HTTP query string processing and dynamic content.
When parsing the boundary string of an HTTP request, the length of that boundary string is not checked before it is copied to a buffer on the heap with a length of 72 bytes. The calculated value of len is not checked before the call to Str_Copy_N [0].
File: http-s_req.c
1661: p_val++; /* Remove space before boundary val. */
1662: p_val = HTTP_StrGraphSrchFirst(p_val,
1663: len);
1664: len = p_field_end - p_val;
1665:
1666: /* Copy boundary val to Conn struct. */
1667: Str_Copy_N(p_conn->FormBoundaryPtr, /* [0] */
1668: p_val,
1669: len);
Because of the memory layout implemented by the uC-LIB Memory Library, this buffer overflow results in an arbitrary allocation controlled by the attacker, which could be used to gain code execution as explained below.
When a heap object is freed using uC-LIB Memory Mem_DynPoolBlkFree, the pointer to the next free chunk of memory within that pool is stored in the first 4 bytes of that memory block [0].
File: lib_mem.c
2072: void Mem_DynPoolBlkFree (MEM_DYN_POOL *p_pool,
2073: void *p_blk,
2074: LIB_ERR *p_err)
2075: {
...
2109: *((void **)p_blk) = p_pool->BlkFreePtr; /* [0] */
So, when this buffer overflow occurs and the following heap block has been allocated and freed previously, this will overwrite the next free pointer address. On the next allocation of the heap pool that contains the overwritten address, that overwritten address will be dereferenced and stored in the pool object as the next free pointer [1]. The attacker can choose where to point the overwritten address anywhere in the address space of the program, including a packet containing attacker-supplied data. On the next call to Mem_DynPoolBlkGet, the dereferenced attacker-controlled value will be the pointer which is allocated [0]. The result of this is that the attacker has the ability to allocate memory at an arbitrary address. The impact of an attacker being able to allocate an arbitrary address is that now the attacker can write data anywhere in the program memory space, which could lead to things like overwriting stack data or a function pointer in order to gain code execution.
File: lib_mem.c
1978: void *Mem_DynPoolBlkGet (MEM_DYN_POOL *p_pool,
1979: LIB_ERR *p_err)
1980: {
...
2014: p_blk = p_pool->BlkFreePtr; /* [0] */
2015: p_pool->BlkFreePtr = *((void **)p_blk); /* [1] */
Program received signal SIGSEGV, Segmentation fault.
0x5656942a in Mem_DynPoolBlkGet (p_pool=0x56576578 <Mem_Heap+408>, p_err=0xffffd3bc) at uc-lib/lib_mem.c:2015
2015 p_pool->BlkFreePtr = *((void **)p_blk);
(gdb) i r
eax 0x41414141 1094795585
ecx 0x56577223 1448571427
edx 0x2 2
ebx 0x56575f64 1448566628
esp 0xffffd370 0xffffd370
ebp 0xffffd388 0xffffd388
esi 0xf7f91000 -134672384
edi 0xf7f91000 -134672384
eip 0x5656942a 0x5656942a <Mem_DynPoolBlkGet+124>
eflags 0x10206 [ PF IF RF ]
cs 0x23 35
ss 0x2b 43
ds 0x2b 43
es 0x2b 43
fs 0x0 0
gs 0x63 99
k0 0x0 0
k1 0x0 0
k2 0x0 0
k3 0x0 0
k4 0x0 0
k5 0x0 0
k6 0x0 0
k7 0x0 0
(gdb) bt
#0 0x5656942a in Mem_DynPoolBlkGet (p_pool=0x56576578 <Mem_Heap+408>, p_err=0xffffd3bc)
at uc-lib/lib_mem.c:2015
#1 0x56563f36 in HTTPsMem_ReqHdrGet (p_instance=0x565763fc <Mem_Heap+28>,
p_conn=0x56576928 <Mem_Heap+1352>, hdr_field=HTTP_HDR_FIELD_ACCEPT_ENCODING,
val_type=HTTP_HDR_VAL_TYPE_STR_DYN, p_err=0xffffd48c) at Server/Source/http-s_mem.c:2141
#2 0x5655a1f2 in HTTPsReq_HdrParse (p_instance=0x565763fc <Mem_Heap+28>, p_conn=0x56576928 <Mem_Heap+1352>,
p_err=0xffffd48c) at Server/Source/http-s_req.c:1780
#3 0x56558c49 in HTTPsReq_Handle (p_instance=0x565763fc <Mem_Heap+28>, p_conn=0x56576928 <Mem_Heap+1352>)
at Server/Source/http-s_req.c:325
#4 0x5655c97a in HTTPsConn_Process (p_instance=0x565763fc <Mem_Heap+28>) at Server/Source/http-s_conn.c:166
#5 0x5655ecfc in HTTPsTask_InstanceTaskHandler (p_instance=0x565763fc <Mem_Heap+28>)
at Server/Source/http-s_task.c:814
#6 0x5655ea62 in HTTPsTask_InstanceTask (p_data=0x565763fc <Mem_Heap+28>) at Server/Source/http-s_task.c:653
#7 0x5656680d in KAL_TaskCreate (task_handle=..., p_fnct=0x5655ea3d <HTTPsTask_InstanceTask>,
p_task_arg=0x565763fc <Mem_Heap+28>, prio=17 '\021', p_cfg=0x0, p_err=0xffffd5e0)
at uc-shims/Source/kal-shim.c:59
#8 0x5655e781 in HTTPsTask_InstanceTaskCreate (p_instance=0x565763fc <Mem_Heap+28>, p_err=0xffffd654)
at Server/Source/http-s_task.c:331
#9 0x5655c179 in HTTPs_InstanceStart (p_instance=0x565763fc <Mem_Heap+28>, p_err=0xffffd654)
at Server/Source/http-s.c:812
#10 0x56557e2b in main (argc=1, argv=0xffffd714) at server_app.c:118
This vulnerability can be mitigated by disabling form and multipart form processing in your application. Disabling this requires changes to the configuration header and the instance configuration file as noted below:
File: http-s_cfg.h
147: /*
148: *********************************************************************************************************
149: * HTTP SERVER FORM CONFIGURATION
150: *
151: * Note(s) : (1) Configure HTTPs_CFG_FORM_EN to enable/disable Form processing source code.
152: *
153: * (2) Configure HTTPs_CFG_FORM_MULTIPART_EN to enable/disable multipart Form processing source code.
154: *********************************************************************************************************
155: */
156:
157: /* Configure Form processing feature (see Note #1): */
158: #define HTTPs_CFG_FORM_EN DEF_DISABLED
159: /* DEF_DISABLED Form processing DISABLED */
160: /* DEF_ENABLED Form processing ENABLED */
161:
162: /* Configure Multipart Form processing feature ... */
163: /* ... (see Note #2): */
164: #define HTTPs_CFG_FORM_MULTIPART_EN DEF_DISABLED
165: /* DEF_DISABLED Mutlipart Form processing DISABLED */
166: /* DEF_ENABLED Mutlipart Form processing ENABLED */
File: app_basic_http-s_instance_cfg.c
328: *--------------------------------------------------------------------------------------------------------
329: * INSTANCE FORM CONFIGURATION
330: *--------------------------------------------------------------------------------------------------------
331: */
332:
333: DEF_NULL, /* .FormCfgPtr : Pointer to Form Cfg Object. */
Another mitigation option is to modify the code within uC-HTTP itself by passing the size used to allocate the buffer FormBoundaryPtr to the size parameter of Str_Copy_N.
diff --git a/Server/Source/http-s_mem.c b/Server/Source/http-s_mem.c
index be6d3e8..a955963 100644
--- a/Server/Source/http-s_mem.c
+++ b/Server/Source/http-s_mem.c
@@ -49,15 +49,6 @@
#define HTTPs_CFG_POOLS_INIT_NBR 1
-/*
-*********************************************************************************************************
-* FORM DEFINES
-*********************************************************************************************************
-*/
-
-#define HTTPs_FORM_BOUNDARY_STR_LEN_MAX 72u
-
-
/*
*********************************************************************************************************
*********************************************************************************************************
diff --git a/Server/Source/http-s_mem.h b/Server/Source/http-s_mem.h
index dfd95b2..c2a0c2e 100644
--- a/Server/Source/http-s_mem.h
+++ b/Server/Source/http-s_mem.h
@@ -144,6 +144,14 @@ void HTTPsMem_RespHdrRelease (HTTPs_INSTANCE *
HTTPs_CONN *p_conn);
#endif
+/*
+*********************************************************************************************************
+* FORM DEFINES
+*********************************************************************************************************
+*/
+
+#define HTTPs_FORM_BOUNDARY_STR_LEN_MAX 72u
+
/*
*********************************************************************************************************
diff --git a/Server/Source/http-s_req.c b/Server/Source/http-s_req.c
index d487160..fedcf47 100644
--- a/Server/Source/http-s_req.c
+++ b/Server/Source/http-s_req.c
@@ -1668,7 +1668,7 @@ static void HTTPsReq_HdrParse (HTTPs_INSTANCE *p_instance,
/* Copy boundary val to Conn struct. */
Str_Copy_N(p_conn->FormBoundaryPtr,
p_val,
- len);
+ HTTPs_FORM_BOUNDARY_STR_LEN_MAX);
/* Make sure to create a string. */
p_conn->FormBoundaryPtr[len] = ASCII_CHAR_NULL;
2023-03-29 - Vendor Disclosure
2023-06-23 - Vendor Patch Release
2023-11-14 - Public Release
Discovered by Kelly Leuschner of Cisco Talos.