CVE-2021-23437 | Regular Expression Denial of Service (ReDoS)

Exp

The package pillow 5.2.0 and before 8.3.2 are vulnerable to Regular Expression Denial of Service (ReDoS) via the getrgb function.

Published: 2021-09-03 Last update: 2026-06-16 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2021-23437 is rated High Exploit Risk (75.3/100): CVSS High severity, with medium exploitation likelihood (EPSS 3.18%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2021-23437

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2021-23437

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-30 3.09% 3.18% +0.09%
2 2026-06-27 2.88% 3.09% +0.22%
3 2026-06-15 — 2.88% —

Full EPSS history (22 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2021-23437

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: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: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:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: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: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:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:N/I:N/A:P Click to expand
Access vector (AV:N)
Can be exploited remotely over network reachability.
Access complexity (AC:L)
Exploitation conditions are straightforward and predictable.
Authentication (AU:N)
No authentication is required.
Confidentiality impact (C:N)
No confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:P)
Partial availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2021-23437

GitHub Security Advisory for CVE-2021-23437

GHSA-98vv-pw6r-q6q4 · Severity: high · Ecosystem: pip — Uncontrolled Resource Consumption in pillow

OS Trackers for CVE-2021-23437

vendor priority summary link
alpine — CVE-2021-23437: 2 source package rows (py-pillow, py3-pillow); 10 state rows across 10 repos (3.11-main, 3.12-main, 3.17-community, 3.18-community, 3.19-community, 3.20-community, 3.21-community, 3.22-community, edge-community, edge-main); fixed 10, open 0. https://security.alpinelinux.org/vuln/CVE-2021-23437
debian not yet assigned CVE-2021-23437 not yet assigned priority: Debian including 1 source packages (pillow), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2021-23437
gentoo high CVE-2021-23437: 1 GLSA(s) (202211-10), 1 atom(s) (dev-python/pillow); latest impact high. https://bugs.gentoo.org/buglist.cgi?quicksearch=CVE-2021-23437
redhat medium — https://access.redhat.com/security/cve/CVE-2021-23437
suse high CVE-2021-23437 severity important: SUSE including 23 source package names (python-Pillow, python-Pillow-4.2.1-3.20.2, …), 48 product×package rows across 18 product lines (HPE Helion OpenStack 8, SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS, … (18 product lines)): Fixed 27, Known Not Affected 21. https://www.suse.com/security/cve/CVE-2021-23437/
ubuntu low CVE-2021-23437 low priority: Ubuntu including 3 source packages (pillow, pillow-python2, python-imaging), 45 status rows across 15 suites (bionic, focal, hirsute, impish, jammy, kinetic, lunar, mantic, noble, oracular, plucky, questing, trusty, upstream, xenial): DNE 27, released 15, needs-triage 3. https://ubuntu.com/security/CVE-2021-23437

Affected software / configurations for CVE-2021-23437

Vendor Product Version Raw CPE
python pillow >= 5.2.0, < 8.3.2 cpe:2.3:a:python:pillow:*:*:*:*:*:*:*:*
fedoraproject fedora 33 cpe:2.3:o:fedoraproject:fedora:33:*:*:*:*:*:*:*
fedoraproject fedora 34 cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*

References for CVE-2021-23437

cvelogic Threat Intelligence