What is CVE-2010-3765?A critical-severity flaw criminals are using now.
CVE-2010-3765 is a critical-severity flaw (CVSS 9.8) in Firefox from Mozilla, published on 28 October 2010. It is on the list of flaws known to be exploited, so criminals are already using it. The latest forecast puts its chance of use in the next 30 days at 83%. If you run an affected version, patch it first.
Published 28 October 2010. Record last updated 22 October 2025. We keep this page's data up to date.
What is CVE-2010-3765? In plain terms.
It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.
Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x before 2.0.10, when JavaScript is enabled, allows remote attackers to execute arbitrary code via vectors related to nsCSSFrameConstructor::ContentAppended, the appendChild method, incorrect index tracking, and the creation of multiple frames, which triggers memory corruption, as exploited in the wild in October 2010 by the Belmoo malware.
What kind of flaw is it?
- CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer
How an attack on it works
Read straight from its severity rating, translated out of the shorthand.
- Where an attacker can beAnywhere on the internet
- How hard it is to pull offEasy: no special conditions
- Login needed firstNo login needed
- Does someone have to clickNo, nobody has to do anything
- What an attacker getsCan read data, change data and take it offline
Severity vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Is CVE-2010-3765 being exploited? Yes.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 83%.
Timeline
- Published
- Added to the known-exploited list
- Record last updated
CVE-2010-3765 scores 90. Action: Emergency patch.
We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:
- Evidence it is being exploitedBiggest factor
- How severe it isStrong factor
- How widely exposed it isSmaller factor
- Threat activity around itSmaller factor
85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.
When CVE-2010-3765 matches software you track, it lands in your list with its score and the reasons behind it.
See your own ranked list →Who is affected by CVE-2010-3765? 3 products.
The published record lists 3 products from 1 vendor. If you run one of these, check your version, then go to the fix below.
- Application
Firefox
by Mozilla
Affected versions3.53.5.13.5.23.5.33.5.43.5.53.5.63.5.73.5.83.5.93.5.103.5.113.5.123.5.13 - Application
Seamonkey
by Mozilla
Affected versions2.0-alpha_12.0-alpha_22.0-alpha_32.0-beta_12.0-beta_22.0-rc1 - Application
Thunderbird
by Mozilla
Affected versions3.0.13.0.23.0.33.0.43.0.53.0.6
How do I fix CVE-2010-3765? Four steps.
- Check whether you run itCompare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
- Apply the vendor’s fixInstall the update named in the vendor’s advisory. We’ve put the advisories and patch notes first in the list.
- If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
- Check it wasn’t used before you patchedBecause criminals are already using this flaw, look for signs of a break-in on affected systems using the vendor’s guidance.
References
50 linksDoes CVE-2010-3765 affect you? We'll keep checking.
Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.
- Tell us what you runPick your software from a list, or let us work it out from your website.
- We match it to every flawOver 400,000 published flaws, checked against your list.
- Ranked by real-world riskA 0 to 100 score, led by evidence criminals are using it.
- Told as soon as we knowAn alert by email, in the app or by webhook to your own tools.
Free plan, no card needed. Nothing to install.
1 flaw being exploited affects software Acme tracks
Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before 3.1.6 and 3.0.x before 3.0.10, and SeaMonkey 2.x before 2.0.10, when ...
- Matched to
- Firefox on Acme's software list
- What to do
- Patch first, then check for signs of use
Sent to the alert recipients Acme chose. Also in the app and to Acme's webhook.
CVE-2010-3765 is a critical-severity flaw in Firefox from Mozilla, published on 28 October 2010. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything. If it works, the attacker can read data, change data and take it offline.
It scores 9.8 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2010-3765 is 90 out of 100, which is Critical. Its action is "Emergency patch". Attackers are using this flaw today. If you run an affected version, it goes to the top of your list.
Attackers are already using it. It is on the government list of flaws known to be exploited, and the latest forecast puts the chance of it being used in the next 30 days at 83%.
For Firefox from Mozilla: 3.5, 3.5.1, 3.5.2, 3.5.3, 3.5.4, 3.5.5 and 19 more. The record lists 3 products in all, each with its versions, under "Who is affected" on this page.
Install the update the vendor names in its advisory, linked first under "How do I fix" on this page. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet. Because criminals are already using it, also check affected systems for signs of a break-in.