CVE-2021-3935 [High] | Security Vulnerability in Pgbouncer

When PgBouncer is configured to use "cert" authentication, a man-in-the-middle attacker can inject arbitrary SQL queries when a connection is first established, despite the use of TLS certificate verification and encryption. This flaw affects PgBouncer versions prior to 1.16.1.

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2025-12-03	0.23%	0.14%	-0.09%
2	2025-11-21	0.47%	0.23%	-0.23%
3	2025-11-18	—	0.47%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2025-12-03

0.23%

0.14%

-0.09%

2025-11-21

0.47%

0.23%

-0.23%

2025-11-18

—

0.47%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
8.1	3.1	HIGH	`CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H` 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:H) Serious risk that confidential data gets exposed in a big way. Integrity (I:H) They could widely tamper with or forge data—trust in the data is badly hurt. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	2.2	5.9	[email protected]
5.1	2.0	MEDIUM	`AV:N/AC:H/Au:N/C:P/I:P/A:P` Click to expand Access vector (AV:N) Can be exploited remotely over network reachability. Access complexity (AC:H) Exploitation requires uncommon or highly specific conditions. Authentication (AU:N) No authentication is required. Confidentiality impact (C:P) Partial confidentiality impact. Integrity impact (I:P) Partial integrity impact. Availability impact (A:P) Partial availability impact.	4.9	6.4	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

8.1

3.1

HIGH

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H 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:H): Serious risk that confidential data gets exposed in a big way.
Integrity (I:H): They could widely tamper with or forge data—trust in the data is badly hurt.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

2.2

5.9

[email protected]

5.1

2.0

MEDIUM

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

Access vector (AV:N): Can be exploited remotely over network reachability.
Access complexity (AC:H): Exploitation requires uncommon or highly specific conditions.
Authentication (AU:N): No authentication is required.
Confidentiality impact (C:P): Partial confidentiality impact.
Integrity impact (I:P): Partial integrity impact.
Availability impact (A:P): Partial availability impact.

4.9

6.4

[email protected]

OS Trackers for CVE-2021-3935

vendor	priority	summary	link
`alpine`	—	CVE-2021-3935: 1 source package rows (pgbouncer); 6 state rows across 6 repos (3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community); fixed 6, open 0.	https://security.alpinelinux.org/vuln/CVE-2021-3935
`debian`	not yet assigned	CVE-2021-3935 not yet assigned priority: Debian including 1 source packages (pgbouncer), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2021-3935
`ubuntu`	medium	CVE-2021-3935 medium priority: Ubuntu including 1 source packages (pgbouncer), 15 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): not-affected 6, ignored 4, needs-triage 4, released 1.	https://ubuntu.com/security/CVE-2021-3935

Affected software / configurations for CVE-2021-3935

Vendor	Product	Version	Raw CPE
pgbouncer	pgbouncer	< 1.16.1	cpe:2.3:a:pgbouncer:pgbouncer::::::::
redhat	enterprise_linux	7.0	cpe:2.3:o:redhat:enterprise_linux:7.0:::::::*
fedoraproject	fedora	35	cpe:2.3:o:fedoraproject:fedora:35:::::::*
debian	debian_linux	9.0	cpe:2.3:o:debian:debian_linux:9.0:::::::*

References for CVE-2021-3935

URL	Tags
http://www.pgbouncer.org/changelog.html#pgbouncer-116x	Release Notes Vendor Advisory
https://bugzilla.redhat.com/show_bug.cgi?id=2021251	Issue Tracking Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/02/msg00016.html	Mailing List Third Party Advisory
https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/TNPCV3KRDI5PLLLKADFVIOHACQJLZMLI/
https://lists.debian.org/debian-lts-announce/2025/05/msg00032.html

URL

CVE-2021-3935

Exploit prediction scoring system (EPSS) score for CVE-2021-3935

Common vulnerability scoring system (CVSS) metrics for CVE-2021-3935

Weakness enumeration for CVE-2021-3935

OS Trackers for CVE-2021-3935

Affected software / configurations for CVE-2021-3935

References for CVE-2021-3935