CVE-2019-20637

An issue was discovered in Varnish Cache before 6.0.5 LTS, 6.1.x and 6.2.x before 6.2.2, and 6.3.x before 6.3.1. It does not clear a pointer between the handling of one client request and the next request within the same connection. This sometimes causes information to be disclosed from the connection workspace, such as data structures associated with previous requests within this connection or VCL-related temporary headers.

Published: 2020-04-08 Last update: 2024-11-21 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2019-20637 is rated Moderate Risk (57/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.68%). EPSS rose +1.20% over the last day, indicating growing attacker interest. Review affected assets and schedule remediation.

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

Exploit prediction scoring system (EPSS) score for CVE-2019-20637

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 2026-06-15 0.48% 1.68% +1.20%
2 2025-11-21 0.39% 0.48% +0.09%
3 2025-11-18 — 0.39% —

Full EPSS history (14 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2019-20637

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:H/I:N/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: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:N)
Data isn’t meaningfully altered or forged.
Availability (A:N)
Service keeps running; no real outage angle.
 3.9 3.6 [email protected]
5.0 2.0 MEDIUM
AV:N/AC:L/Au:N/C:P/I:N/A:N 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:P)
Partial confidentiality impact.
Integrity impact (I:N)
No integrity impact.
Availability impact (A:N)
No availability impact.
 10.0 2.9 [email protected]

Weakness enumeration for CVE-2019-20637

OS Trackers for CVE-2019-20637

vendor priority summary link
debian not yet assigned CVE-2019-20637 not yet assigned priority: Debian including 1 source packages (varnish), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2019-20637
redhat low — https://access.redhat.com/security/cve/CVE-2019-20637
ubuntu medium CVE-2019-20637 medium priority: Ubuntu including 1 source packages (varnish), 10 status rows across 10 suites (bionic, eoan, focal, groovy, hirsute, impish, jammy, trusty, upstream, xenial): not-affected 6, released 2, ignored 1, needs-triage 1. https://ubuntu.com/security/CVE-2019-20637

Affected software / configurations for CVE-2019-20637

Vendor Product Version Raw CPE
varnish-cache varnish_cache >= 6.1.0, < 6.2.2 cpe:2.3:a:varnish-cache:varnish_cache:*:*:*:*:-:*:*:*
varnish-cache varnish_cache >= 6.3.0, < 6.3.1 cpe:2.3:a:varnish-cache:varnish_cache:*:*:*:*:-:*:*:*
varnish-software varnish_cache >= 6.0.0, < 6.0.5 cpe:2.3:a:varnish-software:varnish_cache:*:*:*:*:lts:*:*:*
opensuse backports_sle 15.0 cpe:2.3:a:opensuse:backports_sle:15.0:sp1:*:*:*:*:*:*
opensuse leap 15.1 cpe:2.3:o:opensuse:leap:15.1:*:*:*:*:*:*:*

References for CVE-2019-20637

cvelogic Threat Intelligence