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CVE-2009-5017

17
FAUCET Score

CVE-2009-5017 describes a cross-site scripting (XSS) bypass vulnerability in Mozilla Firefox versions prior to 3.6 Beta 3. This flaw arises from improper handling of overlong UTF-8 encoding, allowing remote attackers to circumvent XSS protection mechanisms with a specially crafted string. The vulnerability has a CVSS score of 4.3 (medium severity), indicating a network-based attack with medium complexity, requiring no authentication, and resulting in partial integrity impact. There is no evidence of active exploitation, public exploit code (Metasploit, Nuclei, ExploitDB), or significant community discussion or media coverage surrounding this CVE.

Impacted Technologies

VendorProductVersion(s)CPE
<= 3.6CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:*:beta2:*:*:*:*:*:*
3.6CPE matchmatch criteria
cpe:2.3:a:mozilla:firefox:3.6:beta1:*:*:*:*:*:*

CVSS Data

CVSS version used by this source: 2.0

4.3MEDIUM

AV:N/AC:M/Au:N/C:N/I:P/A:N

Confidentiality Impact
NONE
Integrity Impact
PARTIAL
Availability Impact
NONE
Access Vector
NETWORK
Access Complexity
MEDIUM
Authentication
NONE
Exploitability Score
8.6
Impact Score
2.9
CvssVersion
2.0

Exploit Intelligence

EPSS Score
1.87%
Probability of exploitation in next 30 days
EPSS Percentile
77.1%
Percentile rank of EPSS score among Peer Group
As of 2026-07-28
Model: v2026.06.15
This CVE's current EPSS score of 0.0187 is in the 58th percentile among its peer group of 19,958 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.0 Reddit, 0.0 Bluesky, 0.0 Mastodon, and 0.2 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.0 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (9)

mozillapatch availablevia nvd_reference
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 4Fixed in: firefox-0:3.6.4-8.el4
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: devhelp-0:0.12-21.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: esc-0:1.1.0-12.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: firefox-0:3.6.4-8.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: gnome-python2-extras-0:2.14.2-7.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: totem-0:2.16.7-7.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: xulrunner-0:1.9.2.4-10.el5
View patch
redhatpatch availablevia redhat_api
Product: Red Hat Enterprise Linux 5Fixed in: yelp-0:2.16.0-26.el5
View patch

Vendor Advisories (1)

redhatCVE-2009-5017Low

Firefox: overlong UTF-8 seqence detection problem

Aug 21, 2009

References

hg.mozilla.org / releases/mozilla-1.9.2/rev/e42c563313a0
bugzilla.mozilla.org / show_bug.cgi
Patch
bugzilla.mozilla.org / show_bug.cgi
sirdarckcat.blogspot.com / 2009/10/couple-of-unicode-issues-on-php-and.html
Exploit