CVE-2021-29991

Description

Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two separate headers. This allowed for a header splitting attack against servers using HTTP/3. This vulnerability affects Firefox < 91.0.1 and Thunderbird < 91.0.1.

Category

8.1
CVSS
Severity: High
CVSS 3.1 •
CVSS 2.0 •
EPSS 0.34%
Vendor Advisory mozilla.org
Affected: Mozilla Firefox
Affected: Mozilla Thunderbird
Published at:
Updated at:

References

Link Tags
https://www.mozilla.org/security/advisories/mfsa2021-37/ vendor advisory
https://bugzilla.mozilla.org/show_bug.cgi?id=1724896 permissions required

Frequently Asked Questions

What is the severity of CVE-2021-29991?
CVE-2021-29991 has been scored as a high severity vulnerability.
How to fix CVE-2021-29991?
To fix CVE-2021-29991, make sure you are using an up-to-date version of the affected component(s) by checking the vendor release notes. As for now, there are no other specific guidelines available.
Is CVE-2021-29991 being actively exploited in the wild?
As for now, there are no information to confirm that CVE-2021-29991 is being actively exploited. According to its EPSS score, there is a ~0% probability that this vulnerability will be exploited by malicious actors in the next 30 days.
What software or system is affected by CVE-2021-29991?
CVE-2021-29991 affects Mozilla Firefox, Mozilla Thunderbird.
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