apcupsd through 3.14.14 discloses uninitialized stack memory in getupsvar() in src/cgi/upsfetch.c (used by upsstats.cgi, multimon.cgi, and upsfstats.cgi. On the single-field path, when the matched STATUS line has fewer than three whitespace-separated tokens, sscanf(%*s %*s %s, answer) performs no assignment but the function returns success, and thus the caller prints the uninitialized destination buffer into the HTTP response.
Weakness
The code uses a variable that has not been initialized, leading to unpredictable or unintended results.