CVE-2026-77421
Description
A flaw was found in the JLine built-in nano editor's regular expression (regex) search mode. A remote attacker could exploit this by providing a specially crafted search term. This could lead to excessive central processing unit (CPU) consumption, causing the editor session to become unresponsive and potentially leading to a denial of service (DoS) for affected users or worker threads in multi-user deployments.
Statement
Red Hat rates this issue as Moderate severity for the following reasons:
Conditions for exploitation: This vulnerability requires an authenticated user to actively type or paste a specially crafted regular expression into the JLine built-in nano editor's search prompt. Unlike a configuration-based attack, the malicious input must be provided interactively during a live editor session. Red Hat's CVSS score reflects this by including UI:R (User Interaction Required), which differs from the upstream CNA score that omits it.
Impact limitations: Successful exploitation results only in a Denial of Service (DoS) through excessive CPU consumption on the editor session thread. There is no impact on data confidentiality or integrity. In single-user scenarios, only the attacker's own session is blocked; in multi-user deployments a worker thread per affected session may be lost, but this does not compromise system-level availability.
Mitigation
Do not expose the JLine built-in nano editor to untrusted users. If applications embedding JLine must provide an interactive editor, disable the regex search mode or restrict editor access to authenticated and trusted users only.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.7 | N/A | 6.5 |
| Attack Vector | Network | N/A | Network |
| Attack Complexity | Low | N/A | Low |
| Privileges Required | Low | N/A | Low |
| User Interaction | Required | N/A | None |
| Scope | Unchanged | N/A | Unchanged |
| Confidentiality | None | N/A | None |
| Integrity Impact | None | N/A | None |
| Availability Impact | High | N/A | High |
Vector
Red Hat: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:N/I:N/A:H
cve.org: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Availability
Technical Impact: DoS: Resource Consumption (CPU)
Attackers can create crafted inputs that intentionally cause the regular expression to use excessive backtracking in a way that causes the CPU consumption to spike.
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