# Possible Information Leak / Session Hijack Vulnerability in Rack

Advisory record · `GHSA-hrqr-hxpp-chr3`

- **Identifiers:** `GHSA-hrqr-hxpp-chr3` · `CVE-2019-16782`
- **State:** Confirmed
- **Severity:** CVSS 6.3 Medium
- **Critical:** No
- **Weakness (CWE):** [CWE-203](https://cwe.mitre.org/data/definitions/203.html) · [CWE-208](https://cwe.mitre.org/data/definitions/208.html)
- **Tags:** [Information disclosure](https://agentprime.io/advisories/tag/info-disclosure.md) · [CWE-208](https://agentprime.io/advisories/tag/cwe-208.md)
- **Published:** 18 Dec 2019
- **Updated:** 10 Sept 2026
- **Reviewed by a person:** No

Published by the GitHub Advisory Database at 18 Dec 2019, 19:01 UTC. agentprime has not analysed this yet, so whether it affects any app is not known.

## Affected packages

- `rack` (RubyGems): affected `<1.6.12 || >=2.0.0, <2.0.8`; fixed in `1.6.12`, `2.0.8`

## Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

> Rack versions below 1.6.12, and versions from 2.0.0 up to but not including 2.0.8, are vulnerable to a timing attack on session ids. An attacker who can send many requests and precisely measure response times could determine a valid session id and hijack that session. Upgrade to Rack 1.6.12 or 2.0.8. The source lists no workarounds.

Written 8 Nov 2026.

## Not analysed yet

We haven’t published our analysis of this Advisory yet. Once a person has reviewed it, this page will say what’s vulnerable, what has to be true for your app to be affected, and how to check.

## Severity and exploitation

- 6.3 Medium, CVSS 3.1: `CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:C/C:H/I:N/A:N`, from CNA (GitHub_M)

- **CISA KEV:** Not listed.
- **EPSS:** 0.037, the 89th percentile, on 8 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

## Timeline

- 18 Dec 2019, 18:16 UTC: [Published by the maintainers as a GitHub repository advisory](https://github.com/rack/rack/security/advisories/GHSA-hrqr-hxpp-chr3)
- 31 Oct 2026, 15:16 UTC: First seen by agentprime
- 31 Oct 2026, 15:16 UTC: [Confirmed by OSV](https://osv.dev/vulnerability/GHSA-hrqr-hxpp-chr3)

## Sources

- [GitHub Advisory Database: GHSA-hrqr-hxpp-chr3](https://github.com/advisories/GHSA-hrqr-hxpp-chr3)
- [OSV: GHSA-hrqr-hxpp-chr3](https://osv.dev/vulnerability/GHSA-hrqr-hxpp-chr3)
- <https://github.com/rack/rack/security/advisories/GHSA-hrqr-hxpp-chr3>
- <https://nvd.nist.gov/vuln/detail/CVE-2019-16782>
- <https://github.com/rack/rack/commit/7fecaee81f59926b6e1913511c90650e76673b38>
- <https://github.com/rack/rack>
- <https://github.com/rubysec/ruby-advisory-db/blob/master/gems/rack/CVE-2019-16782.yml>
- <https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/HZXMWILCICQLA2BYSP6I2CRMUG53YBLX>
- <https://lists.fedoraproject.org/archives/list/package-announce@lists.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>
- <http://www.openwall.com/lists/oss-security/2019/12/19/3>
- <http://www.openwall.com/lists/oss-security/2020/04/08/1>

Facts on this page come from the GitHub Advisory Database (CC-BY 4.0), OSV and the other sources listed, as published. We don’t reproduce full advisory descriptions, which can contain exploit code.

## Check whether this affects you

A Match means an installed version is in the affected range above. Most don’t affect the app; agentprime hasn’t analysed this one yet.

- With the agentprime MCP server (<https://api.agentprime.io/mcp>), ask your agent to check the project: `check_lockfile` sends a lockfile, `check_packages` a list of installed packages, and both return the Matches and the upgrades that clear them. `get_advisory` returns this record. Setup: <https://agentprime.io/mcp.md>
- In a browser: <https://agentprime.io/check/> reads your lockfile in the browser, never uploading it.
- Whether it touches your code, with file and line: the Claude Code plugin, <https://agentprime.io/plugin.md>
- As JSON: <https://api.agentprime.io/v1/advisories/GHSA-hrqr-hxpp-chr3>, or `POST https://api.agentprime.io/v1/match` with your packages (<https://agentprime.io/api.md>)

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The web page: <https://agentprime.io/advisories/GHSA-hrqr-hxpp-chr3/>. Everything for agents: <https://agentprime.io/llms.txt>.