CVE-2021-22890 [Low] | Security Vulnerability in Libcurl

curl 7.63.0 to and including 7.75.0 includes vulnerability that allows a malicious HTTPS proxy to MITM a connection due to bad handling of TLS 1.3 session tickets. When using a HTTPS proxy and TLS 1.3, libcurl can confuse session tickets arriving from the HTTPS proxy but work as if they arrived from the remote server and then wrongly "short-cut" the host handshake. When confusing the tickets, a HTTPS proxy can trick libcurl to use the wrong session ticket resume for the host and thereby circumvent the server TLS certificate check and make a MITM attack to be possible to perform unnoticed. Note that such a malicious HTTPS proxy needs to provide a certificate that curl will accept for the MITMed server for an attack to work - unless curl has been told to ignore the server certificate check.

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#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-06-15	0.09%	3.14%	+3.05%
2	2026-03-04	0.15%	0.09%	-0.06%
3	2026-03-01	—	0.15%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-06-15

0.09%

3.14%

+3.05%

2026-03-04

0.15%

0.09%

-0.06%

2026-03-01

—

0.15%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
3.7	3.1	LOW	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:H) Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.2	1.4	[email protected]
4.3	3.1	MEDIUM	`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N` Click to expand Attack vector (AV:N) Could be attacked over the internet or any normal routed network—not just someone sitting at the machine. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:N) No account or special rights needed—anonymous or random user is enough. User interaction (UI:R) A real person has to do something—click, install, enable—otherwise it doesn’t land. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:L) Attackers could change some data, but it’s limited—not everything goes. Availability (A:N) Service keeps running; no real outage angle.	2.8	1.4	134c704f-9b21-4f2e-91b3-4a467353bcc0
4.3	2.0	MEDIUM	`AV:N/AC:M/Au:N/C:N/I:P/A:N` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:M) Exploitation needs some favorable conditions, but not exceptional ones. Authentication (AU:N) No authentication is required. Confidentiality impact (C:N) No confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:N) No availability impact.	8.6	2.9	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

3.7

3.1

LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:H): Even with access, the exploit needs extra luck, timing, or a fussy environment to actually work.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.2

1.4

[email protected]

4.3

3.1

MEDIUM

CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:L/A:N Click to expand

Attack vector (AV:N): Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N): No account or special rights needed—anonymous or random user is enough.
User interaction (UI:R): A real person has to do something—click, install, enable—otherwise it doesn’t land.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:L): Attackers could change some data, but it’s limited—not everything goes.
Availability (A:N): Service keeps running; no real outage angle.

2.8

1.4

134c704f-9b21-4f2e-91b3-4a467353bcc0

4.3

2.0

MEDIUM

AV:N/AC:M/Au:N/C:N/I:P/A:N Click to expand

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:M): Exploitation needs some favorable conditions, but not exceptional ones.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:N): No confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:N): No availability impact.

8.6

2.9

[email protected]

OS Trackers for CVE-2021-22890

vendor	priority	summary	link
`alpine`	—	CVE-2021-22890: 1 source package rows (curl); 8 state rows across 8 repos (3.12-main, 3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 8, open 0.	https://security.alpinelinux.org/vuln/CVE-2021-22890
`debian`	not yet assigned	CVE-2021-22890 not yet assigned priority: Debian including 1 source packages (curl), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-22890
`gentoo`	high	CVE-2021-22890: 1 GLSA(s) (202105-36), 1 atom(s) (net-misc/curl); latest impact high.	https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-22890
`redhat`	low	—	https://access.redhat.com/security/cve/CVE-2021-22890
`suse`	medium	CVE-2021-22890 severity moderate: SUSE including 358 source package names (0.21.0.3.2.10:libcurl4-7.66.0-4.14.1, 0.38.1.5.8.40:libcurl4-7.66.0-4.14.1, …), 578 product×package rows across 167 product lines (Container bci/bci-init, Container bci/dotnet-aspnet, … (167 product lines)): Fixed 348, Known Affected 141, Known Not Affected 89.	https://www.suse.com/security/cve/CVE-2021-22890/
`ubuntu`	medium	CVE-2021-22890 medium priority: Ubuntu including 1 source packages (curl), 6 status rows across 6 suites (bionic, focal, groovy, trusty, upstream, xenial): not-affected 3, released 2, needs-triage 1.	https://ubuntu.com/security/CVE-2021-22890

Affected software / configurations for CVE-2021-22890

Vendor	Product	Version	Raw CPE
haxx	libcurl	>= 7.63.0, <= 7.75.0	cpe:2.3:a:haxx:libcurl::::::::
fedoraproject	fedora	32	cpe:2.3:o:fedoraproject:fedora:32:::::::*
fedoraproject	fedora	33	cpe:2.3:o:fedoraproject:fedora:33:::::::*
fedoraproject	fedora	34	cpe:2.3:o:fedoraproject:fedora:34:::::::*
netapp	hci_management_node	—	cpe:2.3:a:netapp:hci_management_node:-:::::::*
netapp	solidfire	—	cpe:2.3:a:netapp:solidfire:-:::::::*
netapp	hci_storage_node	—	cpe:2.3:h:netapp:hci_storage_node:-:::::::*
broadcom	fabric_operating_system	—	cpe:2.3:o:broadcom:fabric_operating_system:-:::::::*
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*
siemens	sinec_infrastructure_network_services	< 1.0.1.1	cpe:2.3:a:siemens:sinec_infrastructure_network_services::::::::
oracle	communications_billing_and_revenue_management	12.0.0.3.0	cpe:2.3:a:oracle:communications_billing_and_revenue_management:12.0.0.3.0:::::::*
oracle	essbase	21.2	cpe:2.3:a:oracle:essbase:21.2:::::::*
splunk	universal_forwarder	>= 8.2.0, < 8.2.12	cpe:2.3:a:splunk:universal_forwarder::::::::
splunk	universal_forwarder	>= 9.0.0, < 9.0.6	cpe:2.3:a:splunk:universal_forwarder::::::::
splunk	universal_forwarder	9.1.0	cpe:2.3:a:splunk:universal_forwarder:9.1.0:::::::*

References for CVE-2021-22890

URL	Tags
https://cert-portal.siemens.com/productcert/pdf/ssa-389290.pdf	Patch Third Party Advisory
https://curl.se/docs/CVE-2021-22890.html	Patch Vendor Advisory
https://hackerone.com/reports/1129529	Exploit Issue Tracking Patch Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/2ZC5BMIOKLBQJSFCHEDN2G2C2SH274BP/	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/ITVWPVGLFISU5BJC2BXBRYSDXTXE2YGC/	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/KQUIOYX2KUU6FIUZVB5WWZ6JHSSYSQWJ/	Mailing List Third Party Advisory
https://security.gentoo.org/glsa/202105-36	Third Party Advisory
https://security.netapp.com/advisory/ntap-20210521-0007/	Third Party Advisory
https://www.oracle.com//security-alerts/cpujul2021.html	Third Party Advisory

URL

CVE-2021-22890

Public exploit references (Exploit-DB) for CVE-2021-22890

Exploit prediction scoring system (EPSS) score for CVE-2021-22890

Common vulnerability scoring system (CVSS) metrics for CVE-2021-22890

Weakness enumeration for CVE-2021-22890

OS Trackers for CVE-2021-22890

Affected software / configurations for CVE-2021-22890

References for CVE-2021-22890