N-able on Thursday said it’s investigating a new public disclosure containing claims of additional vulnerabilities in on-premise versions of N-central running version 2026.4.1 HF2.
“Based on our initial review, the server issue described depends on a non-default configuration in which the Legacy API is turned on and exposed to the public internet,” N-able said in a new advisory. “Legacy API is turned off by default in the product and is not recommended.”
The company is urging customers to disable Legacy API immediately, if not already. It also noted that hosted environments are not affected by this issue.
The incident impacts the following services –
- N-central On-premise (Americas)
- N-central On-premise (APAC)
- N-central On-premise (Europe)
The development comes days after N-able released 2026.4.1.26 to address a number of security flaws disclosed by independent security researcher Sean Bales earlier this week. The vulnerabilities are collectively tracked under the name Able2Shell.
The new shortcoming, also revealed by Bales, have been codenamed 4EverAble2Shell and Agent2Shell, adding the proof-of-concept (PoC) exploits successfully work against N-central 2026.4 Hotfix 2 (build 2026.4.1.26), the update N-able released on November 10, 2026, to resolve Able2Shell.
According to the researcher, 4EverAble2Shell enables unauthenticated remote code execution with root privileges on N-central servers. Agent2Shell, on the other hand, leverages more than 10 zero-day vulnerabilities to run commands on managed Windows agents as NT AUTHORITYSYSTEM, assuming the attacker knows the target appliance ID.
Ryan Dewhurst, founder and CEO of Previdian, told The Hacker News that targeted N-central probing has been observed against 4EverAble2Shell within hours following the release of the PoC. The activity has originated from the IP address 157.20.241[.]16. There is no evidence of successful exploitation as of writing.
In the attack chain observed by the threat intelligence company, threat actors have been observed attempting to achieve initial code execution through a recently disclosed Apache Axis flaw (CVE-2026-90436, CVSS score: 9.8), followed by attempts to escalate privileges to root using 4EverAble2Shell, and then download and execute a shell script from 157.20.241[.]16 using curl.
Dewhurst said the development marks the first documented instance of exploitation attempts aimed at CVE-2026-90436, patches for which were released on November 6, 2026.
In a post shared on X, watchTowr also said it’s seeing probes for 4EverAble2Shell targeting N-Centrals builds with the Legacy API enabled.
(This is a developing story. Please check back for more information.)
