CVE-2016-20048: 
Linux Ubuntu vulnerability analysis and mitigation

CVE-2016-20048 is a local stack-based buffer overflow vulnerability in iSelect version 1.4.0-2+b1, a terminal-based interactive selection tool. The flaw allows local attackers to execute arbitrary code by supplying an oversized value to the -k/--key command-line parameter, overflowing a 1024-byte stack buffer. The vulnerability was formally published on March 28, 2026, and assigned by VulnCheck. It carries a CVSS v3.1 base score of 8.4 (High) and a CVSS v4.0 base score of 8.6 (High) (Feedly, VulnCheck Advisory).

The root cause is an out-of-bounds write (CWE-787) resulting from insufficient bounds checking on user-supplied input to the -k/--key parameter. An attacker can craft a malicious command-line argument containing a NOP sled, shellcode, and a crafted return address to overflow the 1024-byte stack buffer and redirect execution flow. No authentication or special privileges are required — only local access to execute the binary. A public proof-of-concept exploit is available on Exploit-DB (Exploit-DB, VulnCheck Advisory).

Successful exploitation allows a local attacker to execute arbitrary code with the privileges of the user running the iSelect binary. This results in high confidentiality, integrity, and availability impact on the affected system. If iSelect is configured with elevated privileges (e.g., setuid), the impact could extend to privilege escalation. The scope is limited to the local system, with no direct lateral movement capability, though code execution could facilitate further post-exploitation activity (Feedly, VulnCheck Advisory).

A public proof-of-concept exploit has been available on Exploit-DB since at least 2017 (exploit ID 41076), making this vulnerability straightforward to weaponize for local attackers (Exploit-DB). The EPSS score is approximately 0.017% (0.000170), indicating a low probability of active exploitation in the wild. There is no evidence of in-the-wild exploitation, threat actor attribution, or inclusion in the CISA Known Exploited Vulnerabilities (KEV) catalog. Detection coverage exists via Tenable Nessus plugin 304208 (Tenable).

1. Reconnaissance: Confirm the target system has iSelect version 1.4.0-2+b1 installed by running iselect --version or checking package manager metadata.
2. Determine buffer size: Identify the 1024-byte stack buffer limit for the -k/--key parameter through source code review or fuzzing.
3. Craft payload: Construct a malicious argument consisting of a NOP sled, architecture-appropriate shellcode (e.g., a local shell spawner), and a crafted return address that redirects execution into the NOP sled.
4. Trigger overflow: Execute iSelect with the oversized -k argument: iselect -k $(python3 -c 'print("\x90"*900 + SHELLCODE + RETURN_ADDR)')
5. Achieve code execution: The stack buffer overflows, the return address is overwritten, and the shellcode executes with the privileges of the invoking user (or elevated privileges if the binary is setuid) (Exploit-DB, VulnCheck Advisory).

• Process: Unusual child processes spawned from iselect (e.g., /bin/sh, /bin/bash) visible in process trees via ps or audit logs.
• Logs: System audit logs (auditd) showing iselect invoked with abnormally long -k argument strings exceeding 1024 characters.
• File System: Unexpected files written to /tmp or user home directories shortly after iSelect execution, potentially indicating shellcode staging or dropped payloads.
• Network: Outbound connections from the host initiated by processes spawned from iselect, particularly to unknown external IPs, if a reverse shell payload is used.

No vendor patch has been publicly announced for iSelect 1.4.0-2+b1 as of the time of this report. Organizations should remove or restrict access to the iSelect binary if it is not required, particularly ensuring it is not configured as setuid. Input validation or wrapper scripts that enforce argument length limits can serve as a temporary workaround. Administrators should monitor for the availability of updated packages from the iSelect project (OSSP iSelect) and apply updates promptly when released.

The vulnerability received limited but notable coverage following its formal CVE publication in March 2026. Security blogs such as InfinitSec published technical write-ups, and automated CVE alert services like RedPacket Security and CVEFeed.io disseminated the advisory (InfinitSec, RedPacket Security). Community reaction was muted given the local-only attack vector and the niche nature of the affected software.