# What is CVE-2026-42523? > CVE-2026-42523 is a critical-severity flaw (CVSS 9.0) in GitHub from Jenkins, published on 29 April 2026. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 0.5%. If you run an affected version, plan in the vendor’s fix. Canonical page: https://www.precursorintelligence.com/what-is/cve-2026-42523 ## At a glance - **Verdict:** Fix this soon. Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month. - **Precursor Intelligence risk score:** 54 out of 100 (Medium); action: Plan remediation. Kept up to date as the evidence changes. - **Severity:** Critical (CVSS 9.0 out of 10) - **Known to be exploited:** No, not on the list of flaws known to be exploited today - **Chance of use in the next 30 days:** 0.5% (latest exploit-likelihood forecast) - **Published:** 29 April 2026 - **Record last updated:** 17 June 2026 - **Main product:** GitHub from Jenkins - **Affected products:** 1 ## What is CVE-2026-42523? In plain terms It can be attacked from anywhere on the internet with an ordinary user account, but a person has to take an action first. If it works, the attacker can read data, change data and take it offline. ### The official description Jenkins GitHub Plugin 1.46.0 and earlier improperly processes the current job URL as part of JavaScript implementing validation of the feature "GitHub hook trigger for GITScm polling", resulting in a stored cross-site scripting (XSS) vulnerability exploitable by non-anonymous attackers with Overall/Read permission. ### What kind of flaw is it? - CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') ### How an attack on it works - Where an attacker can be: Anywhere on the internet - How hard it is to pull off: Easy: no special conditions - Login needed first: An ordinary user account - Does someone have to click: Yes, a person has to take an action - What an attacker gets: Can read data, change data and take it offline Severity vector: `CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H` ## Is CVE-2026-42523 being exploited? Not that we know of It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.5%. That can change at any time, which is why we keep watching. Exploit likelihood over the last 7 days: 0.5%, 0.5%, 0.5%, 0.5%, 0.5%, 0.5%, 0.5%. ### Timeline - 29 April 2026: Published - 17 June 2026: Record last updated ### How Precursor Intelligence ranks it CVE-2026-42523 scores **54 out of 100 (Medium)**, with the action "Plan remediation". Every published flaw gets a risk score from 0 to 100, kept up to date as the evidence changes. Four things go into the score, from the one that counts most to the ones that count less: - Evidence it is being exploited: biggest factor - How severe it is: strong factor - How widely exposed it is: smaller factor - Threat activity around it: smaller factor 85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score. When this flaw matches software you track, it lands in your list with its score and the reasons behind it. ## Who is affected by CVE-2026-42523? The published record lists 1 product. Versions are as published: "before 1.46.0.1" means every version up to, but not including, 1.46.0.1. - [GitHub](https://www.precursorintelligence.com/product/jenkins/github) by [Jenkins](https://www.precursorintelligence.com/vendors/jenkins) (Application): before 1.46.0.1 ## How do I fix CVE-2026-42523? 1. **Check whether you run it.** Compare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list. 2. **Apply the vendor’s fix.** Install the update named in the vendor’s advisory. We’ve put the advisory first in the list. 3. **If you can’t patch today.** Follow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in. 4. **Keep an eye on it.** Track the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood. ### References - [jenkins.io](https://www.jenkins.io/security/advisory/2026-04-29/#SECURITY-3704) (Vendor advisory) ## Questions ### What is CVE-2026-42523? CVE-2026-42523 is a critical-severity flaw in GitHub from Jenkins, published on 29 April 2026. It can be attacked from anywhere on the internet with an ordinary user account, but a person has to take an action first. If it works, the attacker can read data, change data and take it offline. ### How serious is CVE-2026-42523? It scores 9.0 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2026-42523 is 54 out of 100, which is Medium. Its action is "Plan remediation". Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month. ### Is CVE-2026-42523 being exploited? It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 0.5%. That can change at any time, which is why we keep watching. ### Which versions does CVE-2026-42523 affect? For GitHub from Jenkins: before 1.46.0.1. ### How do I fix CVE-2026-42523? Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. ## Does CVE-2026-42523 affect you? Precursor Intelligence keeps checking for you: - **Tell us what you run.** Pick your software from a list, or let us work it out from your website. - **We match it to every flaw.** Over 400,000 published flaws, checked against your list. - **Ranked by real-world risk.** Every flaw gets a 0 to 100 risk score, kept up to date, led by evidence criminals are using it. - **Told as soon as we know.** An alert by email, in the app or by webhook to your own tools. Start free (no card, nothing to install): https://www.precursorintelligence.com/register Book a demo: https://www.precursorintelligence.com/contact