CVE-2021-29651

JWT leak via Open Redirect in Programmatic access

Specific Go Packages Affected

github.com/pomerium/pomerium/proxy

For more information

If you have any questions or comments about this advisory

• Open an issue in pomerium
• Email us at [email protected]

Using programmatic access on protected sites, one can get a signed login URL with pomerium_redirect_uri set to an arbitrary URL. Then, if the user has already logged into Pomerium, they will be redirected to the specified pomerium_redirect_uri with a JWT attached. This allows an outside attacker to get a signed login URL that, upon visiting it, will redirect a victim to the attacker’s site. This creates an issue of Open Redirect and, more seriously, JWT leakage.

With a leaked JWT, the attacker will be able to unveil the victim’s identity (.e.g. email address) by supplying the JWT to the authenticate service or verify.pomerium.com. In addition, if an application integrating Pomerium only verifies the iss claim and others but not the aud claim, the attacker will be able to access it as the victim.

Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites. Typical impact: phishing and credential harvesting via a trusted domain.

CVE-2021-29651 has a CVSS score of 6.3 (Medium). The vector is network-reachable, low privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.13.4); upgrading removes the vulnerable code path.

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Patched in Pomerium v0.13.4

1. What is CVE-2021-29651? CVE-2021-29651 is a medium-severity open redirect vulnerability in github.com/pomerium/pomerium (go), affecting versions < 0.13.4. It is fixed in 0.13.4. Untrusted input controls a URL used for redirection, which can forward users to attacker-controlled sites.
2. How severe is CVE-2021-29651? CVE-2021-29651 has a CVSS score of 6.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of github.com/pomerium/pomerium are affected by CVE-2021-29651? github.com/pomerium/pomerium (go) versions < 0.13.4 is affected.
4. Is there a fix for CVE-2021-29651? Yes. CVE-2021-29651 is fixed in 0.13.4. Upgrade to this version or later.
5. Is CVE-2021-29651 exploitable, and should I be worried? Whether CVE-2021-29651 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2021-29651 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2021-29651? Upgrade github.com/pomerium/pomerium to 0.13.4 or later.

Other vulnerabilities in github.com/pomerium/pomerium