# CVE-2026-77421: JLine: ReDoS in Nano Editor Regex Search Mode

> Attackers can cause denial of service in JLine's nano editor by submitting regex patterns that trigger excessive CPU consumption and block threads.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Sep 2026
- **Updated:** 23 Sep 2026
- **Also known as:** CLEANSTART-2026-AD70544, CLEANSTART-2026-AJ94302, CLEANSTART-2026-EP67643, CLEANSTART-2026-IS00308, CLEANSTART-2026-JE20809, CLEANSTART-2026-YP64784, DEBIAN-CVE-2026-77421, ECHO-ac06-4f09-01e1, GHSA-ph9c-7hw9-vhhw, MINI-33p3-2wqj-f7gj, MINI-68x9-5mfv-9jrp, MINI-6xx2-x297-9659, MINI-7548-ww8q-rf4c, MINI-8hwv-3gmm-j249, MINI-9gp6-5pg5-qqwh, MINI-9w34-6j94-vmx7, MINI-fmg9-rpw9-73gw, MINI-gg44-qpqp-2776, MINI-hwjq-2qr8-jgv3, MINI-jwqv-57qv-jm3f, MINI-r95j-27v8-mhjq, MINI-v2xq-c25q-88fv, MINI-vfxm-f26j-95fq, MINI-vhjh-76f7-gh2h, MINI-w3m4-xr52-qrf5, UBUNTU-CVE-2026-77421

## What is CVE-2026-77421?

CVE-2026-77421 is a medium-severity denial of service vulnerability in jline3, published on 23 Sep 2026. Any signed-in user can exploit it over the network, 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 nano editor's regex search mode passes a user-controlled search term from doSearch(String text) in builtins/src/main/java/org/jline/builtins/Nano.java to Java's backtracking regular expression engine without a timeout or backtracking bound. A nested-quantifier expression evaluated against non-matching buffer content can consume excessive CPU and indefinitely block the editor session thread, and remote multi-user deployments can lose a worker thread for each affected session. 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-2026-77421?

4 open source packages ship an affected version, including org.jline:jline-builtins.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `org.jline:jline-builtins` | Maven | From 3.0.0 | 3.30.15 |
| `org.jline:jline-builtins` | Maven | From 3.0.0 | 3.30.15 |
| `org.jline:jline-builtins` | Maven | From 4.0.0 | 4.3.1 |
| `org.jline:jline-builtins` | Maven | From 4.0.0 | 4.3.1 |

## How do I fix CVE-2026-77421?

Upgrade org.jline:jline-builtins to a fixed version for your release line: 3.30.15 or 4.3.1.

## Is CVE-2026-77421 being exploited?

There is no known exploitation of CVE-2026-77421 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-77421 and fix it if it is affected.

What it is: CVE-2026-77421 is a medium-severity denial of service vulnerability in jline3, published on 23 Sep 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-77421 in the wild and no public exploit code.

Affected packages and fixed versions:
- org.jline:jline-builtins (Maven): affected from 3.0.0; fixed in 3.30.15
- org.jline:jline-builtins (Maven): affected from 3.0.0; fixed in 3.30.15
- org.jline:jline-builtins (Maven): affected from 4.0.0; fixed in 4.3.1
- org.jline:jline-builtins (Maven): affected from 4.0.0; fixed in 4.3.1

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-2026-77421/ (Markdown: https://insights.sbomify.com/CVE-2026-77421/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-77421
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-77421
- OSV: https://osv.dev/vulnerability/CVE-2026-77421

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-77421/
Summaries are generated and may contain mistakes; the official description above is the record.