Submit #855114: Tomato by Shibby Tomato Firmware Tomato v1.28.0000 -120 K26ARM USB AIO-64K Out-of-bounds Write

All three apcupsd CGI programs share a common main() function pattern that reads the configuration file /usr/local/apcupsd/multimon.conf line by line. During parsing, the code performs an out-of-bounds NUL byte write that extends beyond the target stack buffer:

char v26[4096]; // stack buffer
char v27[6]; // adjacent small buffer

fgets(v27, 512, config_file); // reads up to 512 bytes from multimon.conf
v26[strlen(v27) + 4095] = 0; // OOB write when strlen(v27) > 0
The fgets(v27, 512, ...) call reads up to 512 bytes into v27, a 6-byte buffer adjacent to larger stack variables. The subsequent expression v26[strlen(v27) + 4095] = 0 writes a NUL byte at an offset from v26 that depends on the length of the line read. When strlen(v27) > 1, the write exceeds the 4096-byte bound of v26, corrupting adjacent stack data including saved registers and return addresses.

• Source: ⚠️ https://gitee.com/Fengyi-Wang/CVE/issues/IJTQ5N
• User: Anonymous User
• Submission: 06/10/2026 15:56 (1 month ago)
• Moderation: 07/12/2026 23:01 (1 month later)
• Status: Accepted
• VulDB entry: 377895 [Shibby Tomato up to 1.28.0000 apcupsd tomatodata.cgi main out-of-bounds write]
• Points: 20