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CVE-2019-16782: Possible Information Leak / Session Hijack Vulnerability in Rack

• Severity: medium (CVSS 5.9 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 3.7% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2019-12-18 · updated 2026-06-17
• Weakness: CWE-208

Description

There's a possible information leak / session hijack vulnerability in Rack (RubyGem rack). This vulnerability is patched in versions 1.6.12 and 2.0.8. 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.

Affected products

• Fedoraproject Fedora: 31
• openSUSE Leap: 15.1
• rack: before 1.6.12; from 2.0.0 before 2.0.8 — fixed in 1.6.12, 2.0.8
• Rubygems Rack: before 1.6.12; from 2.0.0 before 2.0.8; 0.1.0, 0.2.0, 0.3.0, 0.4.0, 0.9.0, 0.9.1 (+69) — fixed in 1.6.12, 2.0.8

How to fix

Upgrade to a fixed version: rack 1.6.12, 2.0.8; Rubygems Rack 1.6.12, 2.0.8. Check the vendor advisory for mitigations.

References

• http://lists.opensuse.org/opensuse-security-announce/2020-02/msg00016.html
• http://www.openwall.com/lists/oss-security/2019/12/18/2
• http://www.openwall.com/lists/oss-security/2019/12/18/3
• http://www.openwall.com/lists/oss-security/2019/12/19/3
• http://www.openwall.com/lists/oss-security/2020/04/08/1
• http://www.openwall.com/lists/oss-security/2020/04/09/2
• https://github.com/rack/rack/commit/7fecaee81f59926b6e1913511c90650e76673b38
• https://github.com/rack/rack/security/advisories/GHSA-hrqr-hxpp-chr3
• https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HZXMWILCICQLA2BYSP6I2CRMUG53YBLX/
• http://lists.opensuse.org/opensuse-security-announce/2020-02/msg00016.html
• http://www.openwall.com/lists/oss-security/2019/12/18/2
• http://www.openwall.com/lists/oss-security/2019/12/18/3

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