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- Rev 37407 2026-08-26 12:26:43
- Author: amit
- Log message:
- Vivo IMEI activation: log why a captcha was rejected
Production refuses ~56% of submissions, but reading the stored images by hand
showed 9 of 10 carried the CORRECT code. Replicating the request from the same
box gives 85-93%, and every external difference was measured and ruled out:
real vs dummy imei (7/8 both), user-agent (83% both), session reuse (74 vs 75%),
two concurrent jobs (80% both), source IP, and fetch-to-submit delay from 0 to
10s (90-91% throughout). Vivo's reply is byte-identical in every failure, so the
payload carries no discriminator.
That leaves something inside this process, and the old log line recorded five
words and discarded the evidence. It now captures the code submitted, the imei,
the real fetch-to-submit latency, the session cookies actually held at submit
time, and Vivo's full response.
The cookies matter most: if the SESSION cookie is being dropped or rotated
between fetching the captcha and submitting it, the captcha would be validated
against the wrong session and refused despite a correct code -- which fits every
measurement above and is invisible from outside the JVM.