What is CVE-2009-4491?

CVE-2009-4491 is a critical-severity vulnerability in Acme Thttpd, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2010-01-13.

How severe is CVE-2009-4491?

Critical severity. CVSS v3 base score is 9.8 out of 10.

RCE in Acme Thttpd

CVE-2009-4491

thttpd 2.25b0 writes data to a log file without sanitizing non-printable characters, which might allow remote attackers to modify a window's title, or possibly execute arbitrary commands or overwrite files, via an HTTP request containing an escape sequence for a terminal emulator.

Vulnerability class: Drupalgeddon 2 (CVE-2018-7600)

Published 2010-01-13 · last modified 2026-06-16.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.137 (96.4th percentile), scored 2026-09-29.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 96th percentile — 96.4% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.135 · newest: 0.137 · change: +0.003

Affected products

Acme Thttpd — versions 2.25

Weakness classification (CWE)

References

www.ush.it/team/ush/hack_httpd_escape/adv.txt (Exploit)
www.securityfocus.com/archive/1/508830/100/0/threaded (mailing-list)
seclists.org/fulldisclosure/2023/Nov/13 (mailing-list)
packetstormsecurity.com/files/175949/m-privacy-TightGate-Pro-Code-Execution-Ins…

Frequently asked questions

What is CVE-2009-4491?: CVE-2009-4491 is a critical-severity vulnerability in Acme Thttpd, classified under Improper Input Validation. CVSS score: 9.8/10. Published 2010-01-13.
How severe is CVE-2009-4491?: Critical severity. CVSS v3 base score is 9.8 out of 10.