# CVE-2026-15243: Improper Validation of Certificate in CAS Client

> Attackers can bypass certificate validation in Apereo CAS Client to intercept authentication tickets via Man-in-the-Middle attacks.

- **Severity:** High 7.4 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 24 Jul 2026
- **Updated:** 24 Jul 2026
- **Also known as:** GHSA-52jg-6vw4-42p8

## What is CVE-2026-15243?

CVE-2026-15243 is a high-severity vulnerability in Apereo Jasig CAS Client, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

Apereo CAS Client accepts any CA-trusted certificate for any hostname, provided the URL the client is calling matches the configured allowlist or regex. An attacker with a MITM position (DNS poisoning, rogue Wi-Fi, malicious proxy, etc.) can provide any CA-signed certificate for a hostname that matches the configured allowlist or regex. This can lead to intercepting the CAS exchange, capturing the Ticket-Granting Ticket (TGT), and subsequently obtaining Service Tickets on behalf of the victim. 

Because maintainers contact attempts were unsuccessful, vulnerabilities have only been confirmed in version 4.1.0 (Java Apereo CAS Client) and 3.6.4 (Jasig CAS Client) but may also affect other versions.

Weakness: CWE-297 (Improper Validation of Certificate with Host Mismatch)

## Which versions are affected by CVE-2026-15243?


## How do I fix CVE-2026-15243?

No fix has been published for CVE-2026-15243 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-15243 being exploited?

There is no known exploitation of CVE-2026-15243 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-15243 and fix it if it is affected.

What it is: CVE-2026-15243 is a high-severity vulnerability in Apereo Jasig CAS Client, published on 24 Jul 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-15243 in the wild and no public exploit code.

Affected product: Apereo Jasig CAS Client. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-15243/ (Markdown: https://insights.sbomify.com/CVE-2026-15243/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-15243
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-15243
- OSV: https://osv.dev/vulnerability/CVE-2026-15243

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-15243/
Summaries are generated and may contain mistakes; the official description above is the record.