siyuan-note
SiYuan 2.1.0 before 3.8.9 CAPTCHA Bypass via Stale Login Cookie
Not on CISA's list of exploited flaws, and not in the news we track.
CVE-2026-126265Critical9.1
Reading the vendor advisory
Black Shard's team can check your exposure to CVE-2026-126265 and take the fix off your plate.
SiYuan 2.1.0 before 3.8.9 contains a flaw where the loginAuth CAPTCHA challenge lives in a signed client-side cookie, allowing reuse of a solved challenge. Attackers can replay the original signed siyuan cookie with distinct wrong access codes to brute-force the code and gain an administrator session.
Black Shard's team can check your exposure, take a fix off your plate or step in on a live incident.
Severity
9.1of 10, critical
Updated 13 Nov 2026, 12:00 UTC, 30 of 36 sources answering.
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