CVE-2021-43535
HIGH
8.8
CVSS Score
Published: December 8, 2021 at 09:20 PM UTC
Updated: June 17, 2026 at 04:11 AM UTC
4 products affected across 2 vendorsDebian LinuxFirefoxThunderbird
Using Firefox by Mozilla?
Get instant alerts when new vulnerabilities affect Firefox - before attackers find them.
Real-time alertsTrack your software stackFree plan available
Severity
HIGH8.8
Exploit prediction
EPSS 1%
Description
A use-after-free could have occured when an HTTP2 session object was released on a different thread, leading to memory corruption and a potentially exploitable crash. This vulnerability affects Firefox < 93, Thunderbird < 91.3, and Firefox ESR < 91.3.
Affected
Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.
Debian Linux· Debiandrupal
95%v < 93
Affected range stops below 93, so it looks safe — our inference, not a vendor statement
Affected range stops below 93.0, so it looks safe — our inference, not a vendor statement
v < 91.3
Affected range stops below 91.3, so it looks safe — our inference, not a vendor statement
Affected range stops below 91.3.0, so it looks safe — our inference, not a vendor statement
v < 91.3
Affected range stops below 91.3, so it looks safe — our inference, not a vendor statement
Affected range stops below 91.3.0, so it looks safe — our inference, not a vendor statement
Remediation
No guide yetNo remediation guidance has been written for this CVE yet. What the record does show:
References (8)
x_refsource_MISCIssue TrackingPermissions RequiredVendor Advisory
Source: [email protected]
https://bugzilla.mozilla.org/show_bug.cgi?id=1667102Mailing Listx_refsource_MLISTThird Party Advisory
Source: [email protected]
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.htmlMailing Listx_refsource_MLISTThird Party Advisory
Source: [email protected]
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.htmlVendor Advisoryx_refsource_DEBIANThird Party Advisory
Source: [email protected]
https://www.debian.org/security/2021/dsa-5026Vendor Advisoryx_refsource_DEBIANIssue TrackingThird Party Advisory
Source: [email protected]
https://www.debian.org/security/2022/dsa-5034x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-43/x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-49/x_refsource_MISCVendor Advisory
Source: [email protected]
https://www.mozilla.org/security/advisories/mfsa2021-50/CVSS
- Attack Vector
- NETWORK
- Complexity
- LOW
- Privileges
- NONE
- User Interaction
- REQUIRED
- Scope
- UNCHANGED
- Confidentiality
- HIGH
- Integrity
- HIGH
- Availability
- HIGH
Vector?
Quick Info
StatusMODIFIED
CWE
CWE-416
Get alerted
Stop reading CVE feeds looking for your own stack
Track the products you run and VulnTracker tells you when a new CVE affects them — with what is known about fixing it, and nothing about the rest.
Free plan, no card