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Date: Wed, 18 Dec 2019 10:16:02 -0800
From: Aaron Patterson <>
Subject: [CVE-2019-16782] Possible Information Leak / Session Hijack
 Vulnerability in Rack

There is a possible information leak / session hijacking vulnerability
in Rack. This vulnerability has been assigned the CVE identifier

Versions Affected:  All.
Not affected:       None.
Fixed Versions:     1.6.12, 2.0.8

There's a possible information leak / session hijack vulnerability in
Rack. Attackers may be able to find and hijack sessions by using timing
attacks targeting the session id. Session ids are usually stored and
indexed in a database that uses some kind of scheme for speeding up
lookups of that session id. By carefully measuring the amount of time it
takes to look up a session, an attacker may be able to find a valid
session id and hijack the session.

The session id itself may be generated randomly, but the way the session
is indexed by the backing store does not use a secure comparison.


The session id stored in a cookie is the same id that is used when
querying the backing session storage engine. Most storage mechanisms
(for example a database) use some sort of indexing in order to speed up
the lookup of that id. By carefully timing requests and session lookup
failures, an attacker may be able to perform a timing attack to
determine an existing session id and hijack that session.


The 1.6.12 and 2.0.8 releases are available at the normal locations.


There are no known workarounds.


To aid users who aren't able to upgrade immediately we have provided patches for
the two supported release series. They are in git-am format and consist of a
single changeset.

1-6-session-timing-attack.patch - Patch for 1.6 series
2-0-session-timing-attack.patch - Patch for 2.6 series


Thanks Will Leinweber for reporting this!

Aaron Patterson

View attachment "1-6-session-timing-attack.patch" of type "text/plain" (17949 bytes)

View attachment "2-0-session-timing-attack.patch" of type "text/plain" (16516 bytes)

Download attachment "signature.asc" of type "application/pgp-signature" (489 bytes)

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