# CVE-2026-77423: JLine: ReDoS in Built-in Less Viewer Search

> Attackers can cause denial of service in JLine applications by submitting malicious regex patterns to the built-in less viewer, exhausting CPU resources.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Sep 2026
- **Updated:** 24 Sep 2026
- **Also known as:** DEBIAN-CVE-2026-77423, GHSA-2v9w-34q6-wpqx, UBUNTU-CVE-2026-77423

## What is CVE-2026-77423?

CVE-2026-77423 is a high-severity denial of service vulnerability in jline3, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

JLine is a Java library for handling console input. From 3.0.0 until 3.30.15 and 4.3.1, the JLine built-in less viewer passes user-controlled search and display-filter patterns from getPattern(boolean doDisplayPattern) in builtins/src/main/java/org/jline/builtins/Less.java directly to Java's backtracking regular expression engine and repeatedly applies them to file content. A nested-quantifier expression evaluated against non-matching lines can consume excessive CPU and indefinitely block the session thread, and repeated sessions in Telnet or SSH deployments can exhaust a bounded worker pool. This issue is fixed in versions 3.30.15 and 4.3.1.

Weakness: CWE-1333 (Inefficient Regular Expression Complexity)

## Which versions are affected by CVE-2026-77423?


## How do I fix CVE-2026-77423?

No fix has been published for CVE-2026-77423 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-77423 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77423 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77423 and fix it if it is affected.

What it is: CVE-2026-77423 is a high-severity denial of service vulnerability in jline3, published on 23 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-77423 exists.

Affected product: jline3. 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-2026-77423/ (Markdown: https://insights.sbomify.com/CVE-2026-77423/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77423
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77423
- OSV: https://osv.dev/vulnerability/CVE-2026-77423

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77423/
Summaries are generated and may contain mistakes; the official description above is the record.