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Vulnerability details: VCID-2snw-9yc1-t7eb
Vulnerability ID VCID-2snw-9yc1-t7eb
Aliases CVE-2021-43535
Summary 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.
Status Published
Exploitability 0.5
Weighted Severity 8.0
Risk 4.0
Affected and Fixed Packages Package Details
Weaknesses (1)
CWE-416 Use After Free
System Score Found at
cvssv3 8.8 https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-43535.json
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
epss 0.0136 https://api.first.org/data/v1/epss?cve=CVE-2021-43535
cvssv2 6.8 https://nvd.nist.gov/vuln/detail/CVE-2021-43535
cvssv3.1 8.8 https://nvd.nist.gov/vuln/detail/CVE-2021-43535
generic_textual high https://www.mozilla.org/en-US/security/advisories/mfsa2021-43
generic_textual high https://www.mozilla.org/en-US/security/advisories/mfsa2021-49
generic_textual high https://www.mozilla.org/en-US/security/advisories/mfsa2021-50
Reference id Reference type URL
https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-43535.json
https://api.first.org/data/v1/epss?cve=CVE-2021-43535
https://bugzilla.mozilla.org/show_bug.cgi?id=1667102
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38496
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38500
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38502
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38503
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38504
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38506
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38507
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38508
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-38509
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4126
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-4129
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43528
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43529
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43534
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43535
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43536
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43537
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43538
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43539
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43541
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43542
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43543
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43545
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-43546
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-44538
https://lists.debian.org/debian-lts-announce/2021/12/msg00030.html
https://lists.debian.org/debian-lts-announce/2022/01/msg00001.html
https://www.debian.org/security/2021/dsa-5026
https://www.debian.org/security/2022/dsa-5034
https://www.mozilla.org/security/advisories/mfsa2021-43/
https://www.mozilla.org/security/advisories/mfsa2021-49/
https://www.mozilla.org/security/advisories/mfsa2021-50/
2019626 https://bugzilla.redhat.com/show_bug.cgi?id=2019626
cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:mozilla:firefox:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:mozilla:firefox_esr:*:*:*:*:*:*:*:*
cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:a:mozilla:thunderbird:*:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:10.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:* https://nvd.nist.gov/vuln/search/results?adv_search=true&isCpeNameSearch=true&query=cpe:2.3:o:debian:debian_linux:9.0:*:*:*:*:*:*:*
CVE-2021-43535 https://nvd.nist.gov/vuln/detail/CVE-2021-43535
mfsa2021-43 https://www.mozilla.org/en-US/security/advisories/mfsa2021-43
mfsa2021-49 https://www.mozilla.org/en-US/security/advisories/mfsa2021-49
mfsa2021-50 https://www.mozilla.org/en-US/security/advisories/mfsa2021-50
RHSA-2021:4116 https://access.redhat.com/errata/RHSA-2021:4116
RHSA-2021:4123 https://access.redhat.com/errata/RHSA-2021:4123
RHSA-2021:4130 https://access.redhat.com/errata/RHSA-2021:4130
RHSA-2021:4132 https://access.redhat.com/errata/RHSA-2021:4132
RHSA-2021:4133 https://access.redhat.com/errata/RHSA-2021:4133
RHSA-2021:4134 https://access.redhat.com/errata/RHSA-2021:4134
RHSA-2021:4605 https://access.redhat.com/errata/RHSA-2021:4605
RHSA-2021:4607 https://access.redhat.com/errata/RHSA-2021:4607
USN-5248-1 https://usn.ubuntu.com/5248-1/
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Found at https://access.redhat.com/hydra/rest/securitydata/cve/CVE-2021-43535.json
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Vector: AV:N/AC:M/Au:N/C:P/I:P/A:P Found at https://nvd.nist.gov/vuln/detail/CVE-2021-43535
Exploitability (E) Access Vector (AV) Access Complexity (AC) Authentication (Au) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

high

functional

unproven

proof_of_concept

not_defined

local

adjacent_network

network

high

medium

low

multiple

single

none

none

partial

complete

none

partial

complete

none

partial

complete
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H Found at https://nvd.nist.gov/vuln/detail/CVE-2021-43535
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

low

high

none

low

high

none

required

unchanged

changed

high

low

none

high

low

none

high

low

none
Exploit Prediction Scoring System (EPSS)
Percentile 0.79353
EPSS Score 0.0136
Published At July 30, 2025, 12:55 p.m.
Date Actor Action Source VulnerableCode Version
2025-07-31T08:09:46.368271+00:00 Mozilla Importer Import https://github.com/mozilla/foundation-security-advisories/blob/master/announce/2021/mfsa2021-49.yml 37.0.0