TI-2021-10608 Aliases CVE-2021-29991 GHSA-8p2q-73gc-fxq5

Firefox incorrectly accepted a newline in a HTTP/3 header, interpretting it as two…

LOW 37CWE-444Published 2021-11-03 · Updated 2024-08-03

Key facts

Attack vector: Network
Privileges required: None
User interaction: Required
Attack complexity: Low
Impact type: —
Confidentiality · integrity · availability: High · High · None
Fix status: Partial Red Hat: 3 without a fix

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat.

Summary

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.

Why it matters now

EPSS 0.0091 60th percentileScored 2026-11-07

Fix Partial Firefox (Mozilla): 91.0.1Thunderbird (Mozilla): 91.0.1Red Hat: 3 without a fix

SSVC decision points

Not available: CISA has not published SSVC decision points for this record.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
Mozilla	Firefox	before 91.0.1	91.0.1	Patch available	CNA
Mozilla	Thunderbird	before 91.0.1	91.0.1	Patch available	CNA

Firefox VendorMozilla Affected before 91.0.1 Fixed in 91.0.1 Patch available CNA
Thunderbird VendorMozilla Affected before 91.0.1 Fixed in 91.0.1 Patch available CNA

CPE configurations NVD · 2

CPE	Versions	Role	Vendor
cpe:2.3:a:mozilla:firefox::::::::	before 91.0.1	Vulnerable	Mozilla
cpe:2.3:a:mozilla:thunderbird::::::::	before 91.0.1	Vulnerable	Mozilla

cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* Versions before 91.0.1 Vulnerable ·Mozilla
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* Versions before 91.0.1 Vulnerable ·Mozilla

Remediation

Fix · CNA Firefox (Mozilla) Fixed in 91.0.1
Fix · CNA Thunderbird (Mozilla) Fixed in 91.0.1

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 6	Affected	No fix planned: Out of support scope
Red Hat Enterprise Linux 7	Affected	No fix yet: Fix deferred
Red Hat Enterprise Linux 8	Affected	No fix yet: Fix deferred

Not affected: 1 product

Red Hat Enterprise Linux 9

Timeline

2026-10-02 Threatist record created from CVE-2021-29991
2026-10-03 Alias added: GHSA-8p2q-73gc-fxq5

References

Advisory 1

https://www.mozilla.org/security/advisories/mfsa2021-37/

Other 1

https://bugzilla.mozilla.org/show_bug.cgi?id=1724896

TI-2024-08981 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.8
TI-2022-09832 Use after free in Mozilla Firefox KEVCVSS 3.1CRITICAL 9.6
TI-2019-08769 Improper input validation in Mozilla Firefox ESR KEVCVSS 3.1CRITICAL 10.0
TI-2010-03577 Mozilla Firefox 3.5.x through 3.5.14 and 3.6.x through 3.6.11, Thunderbird 3.1.6 before… KEVCVSS 3.1CRITICAL 9.8
TI-2023-04799 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8
TI-2023-04477 Out-of-bounds write in Google Chrome KEVCVSS 3.1HIGH 8.8

See all 3444 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences