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ZDI-06-010: Mozilla Firefox CSS Letter-Spacing Heap Overflow Vulnerability
From: zdi-disclosures () 3com com
Date: Fri, 14 Apr 2006 18:02:40 -0700

ZDI-06-010: Mozilla Firefox CSS Letter-Spacing Heap Overflow Vulnerability
April 13, 2006

-- CVE ID:

-- Affected Vendor:

-- Affected Products:
Mozilla 1.7.x and below
Firefox 1.5.x and below

-- TippingPoint(TM) IPS Customer Protection:
TippingPoint IPS customers have been protected against this
vulnerability since January 31, 2006 by Digital Vaccine protection
filter ID 4097. For further product information on the TippingPoint IPS:


-- Vulnerability Details:
This vulnerability allows attackers to execute arbitrary code on
vulnerable installations of the Mozilla/Firefox web browser. User
interaction is required to exploit this vulnerability in that the
target must visit a malicious page.

The specific flaw is due to incorrect handling of the CSS
"letter-spacing" element. By specifying a large number, an attacker can
overflow an integer used during memory allocation. The under-allocated
buffer is later used to store user-supplied data leading to an
exploitable heap overflow.

-- Vendor Response:
Mozilla has issued an update to correct this vulnerability. Details are
available at:

-- Disclosure Timeline:
2006.01.31 - Vulnerability reported to vendor
2006.01.31 - Digital Vaccine released to TippingPoint customers
2006.04.13 - Coordinated public release of advisory

-- Credit:
This vulnerability was discovered by an anonymous researcher.

-- About the Zero Day Initiative (ZDI):
Established by TippingPoint, a division of 3Com, The Zero Day Initiative
(ZDI) represents a best-of-breed model for rewarding security
researchers for responsibly disclosing discovered vulnerabilities.

Researchers interested in getting paid for their security research
through the ZDI can find more information and sign-up at:


The ZDI is unique in how the acquired vulnerability information is used.
3Com does not re-sell the vulnerability details or any exploit code.
Instead, upon notifying the affected product vendor, 3Com provides its
customers with zero day protection through its intrusion prevention
technology. Explicit details regarding the specifics of the
vulnerability are not exposed to any parties until an official vendor
patch is publicly available. Furthermore, with the altruistic aim of
helping to secure a broader user base, 3Com provides this vulnerability
information confidentially to security vendors (including competitors)
who have a vulnerability protection or mitigation product.

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