How severe is CVE-2009-4491?

CVE-2009-4491 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2009-4491 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 13% (96th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2009-4491?

CVE-2009-4491 affects Acme Thttpd. See the affected-products list for the exact vulnerable versions.

How do I fix CVE-2009-4491?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2009-4491 published?

CVE-2009-4491 was published on 2010-01-13 and last updated on 2026-06-16.

CVE-2009-4491

CVE-2009-4491 is a critical-severity vulnerability in Acme Thttpd with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 13% places it in the 96th percentile, indicating an elevated likelihood of exploitation. The underlying weakness is classified as CWE-20.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 5.0
EPSS exploit prediction: 13% (96th percentile)
Actively exploited: Not listed in CISA KEV
Weakness: CWE-20
Affected product: Acme Thttpd
Published: 2010-01-13
Last modified: 2026-06-16

Description

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.

Frequently asked questions

What is 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.
How severe is CVE-2009-4491?: CVE-2009-4491 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2009-4491 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 13% (96th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2009-4491?: CVE-2009-4491 affects Acme Thttpd. See the affected-products list for the exact vulnerable versions.
How do I fix CVE-2009-4491?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2009-4491 published?: CVE-2009-4491 was published on 2010-01-13 and last updated on 2026-06-16.

References

Affected products (1)

cpe:2.3:a:acme:thttpd:2.25:b:*:*:*:*:*:*

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