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Google DevSite Flask Session Pickle RCE - #3166
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carlospolop merged 2 commits intoOct 21, 2026
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Decision: keep The researcher’s write-up supports the secret exposure, signing-key validation, callback deserialization, and timing controls. Flask source confirms tagged-byte serialization and the escape behavior for a literal tag-shaped dictionary. The base book covers Flask signing and generic pickle risks, but not this nested application-session failure mode. The repaired directory link and heading r… Head: |
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October 21, 2026 17:39
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Blog URL
https://simonkoeck.com/writeups/google-devsite-flask-session-pickle-rce
Blog Title
Google DevSite Flask Session Pickle RCE
Blog high summary
Documents an unauthenticated RCE chain in Google’s shared DevSite Flask OAuth flow. A roughly 1,200-byte client-side cookie exposed an
OAuth2WebServerFlowpickle and reused its OAuthclient_secretas Flask’s signing key; reproducing theitsdangerousHMAC enabled arbitrary session forgery.An attacker-chosen CSRF/state key placed a base64 pickle in the matching flow entry, reaching
pickle.loads();time.sleep(N)via__reduce__yielded 0.207, 3.193, 5.194, and 8.283-second responses, proving callable execution. The recovered key also signed sessions across five DevSite domains. Fixes were secret rotation, isolated keys, server-side flow state, and data-only serialization.PR changes
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