Home Cyber Security News Mozilla Patched “BigSig” Vulnerability That Affects The NSS Cryptographic Library

Mozilla Patched “BigSig” Vulnerability That Affects The NSS Cryptographic Library

by Abeerah Hashim
Mozilla patched BigSig NSS bug

A security researcher from Google Project Zero discovered a critical and easily exploitable “BigSig” vulnerability in Mozilla NSS cryptographic library. Despite being easy to spot and recurrent fuzzing, the flaw escaped the attention of the security team for years.

“BigSig” Bug In NSS Cryptographic Library

Google’s Tavis Ormandy, from the Project Zero team, has shared details about the NSS library vulnerability in a recent post. As elaborated, he found the bug in Mozilla’s famous Network Security Services (NSS) library while “experimenting with alternative methods for measuring code coverage”.

According to Ormandy, Mozilla keeps fuzzing its NSS library, still, this trivial vulnerability escaped their attention. Describing it further, Ormandy stated,

The original code was checked in with ECC support on the 17th October 2003, but wasn’t exploitable until some refactoring in June 2012. In 2017, RSA-PSS support was added and made the same error.

Anyhow, as explained, the researcher’s method to find this bug involved two approaches; stack coverage and object isolation. Nonetheless, the researcher believes that this bug should have caught attention even with “rudimentary fuzzing”.

As elaborated in the bug report, the bug was basically a memory corruption flaw, which the researcher named “BigSig”.

When you verify a digital signature, NSS will create a VFYContext structure to store the necessary data. This includes things like the public key, the hash algorithm, and the signature itself…
The maximum size signature that this structure can handle is whatever the largest union member is, in this case that’s RSA at 2048 bytes. That’s 16384 bits, large enough to accommodate signatures from even the most ridiculously oversized keys.

That’s where the bug (CVE-2021-43527) appeared when the signature exceeds the size.

The untrusted signature is simply copied into this fixed-sized buffer, overwriting adjacent members with arbitrary attacker-controlled data.

The researcher explained that this bug affects multiple algorithms and is easy to reproduce. Describing further about the vulnerable versions, he wrote,

NSS since 3.14 (released October 2012) are vulnerable.

Mozilla Firefox Remains Unaffected

Following the bug report, Mozilla started working on the fix that they have now released with NSS 3.73.0.

In its advisory, Mozilla has confirmed that the vulnerability does not impact the Mozilla Firefox browser. Yet, it does affect other products for which, Mozilla has released the patches.

Email clients and PDF viewers that use NSS for signature verification, such as Thunderbird, LibreOffice, Evolution and Evince are believed to be impacted.

Let us know your thoughts in the comments.

You may also like

Latest Hacking News

Privacy Preference Center

Necessary

The __cfduid cookie is used to identify individual clients behind a shared IP address and apply security settings on a per-client basis.

cookie_notice_accepted and gdpr[allowed_cookies] are used to identify the choices made from the user regarding cookie consent.

For example, if a visitor is in a coffee shop where there may be several infected machines, but the specific visitor's machine is trusted (for example, because they completed a challenge within your Challenge Passage period), the cookie allows Cloudflare to identify that client and not challenge them again. It does not correspond to any user ID in your web application, and does not store any personally identifiable information.

__cfduid, cookie_notice_accepted, gdpr[allowed_cookies]

Advertising

DoubleClick by Google refers to the DoubleClick Digital Marketing platform which is a separate division within Google. This is Google’s most advanced advertising tools set, which includes five interconnected platform components.

DoubleClick Campaign Manager: the ad-serving platform, called an Ad Server, that delivers ads to your customers and measures all online advertising, even across screens and channels.

DoubleClick Bid Manager – the programmatic bidding platform for bidding on high-quality ad inventory from more than 47 ad marketplaces including Google Display Network.

DoubleClick Ad Exchange: the world’s largest ad marketplace for purchasing display, video, mobile, Search and even Facebook inventory.

DoubleClick Search: is more powerful than AdWords and used for purchasing search ads across Google, Yahoo, and Bing.

DoubleClick Creative Solutions: for designing, delivering and measuring rich media (video) ads, interactive and expandable ads.

doubleclick

Analytics

The _ga is asssociated with Google Universal Analytics - which is a significant update to Google's more commonly used analytics service. This cookie is used to distinguish unique users by assigning a randomly generated number as a client identifier. It is included in each page request in a site and used to calculate visitor, session and campaign data for the sites analytics reports. By default it is set to expire after 2 years, although this is customisable by website owners.

The _gat global object is used to create and retrieve tracker objects, from which all other methods are invoked. Therefore the methods in this list should be run only off a tracker object created using the _gat global variable. All other methods should be called using the _gaq global object for asynchronous tracking.

_gid works as a user navigates between web pages, they can use the gtag.js tagging library to record information about the page the user has seen (for example, the page's URL) in Google Analytics. The gtag.js tagging library uses HTTP Cookies to "remember" the user's previous interactions with the web pages.

_ga, _gat, _gid