CVE-2019-20637Network attack vector

Information disclosure via uncleared request error pointer

Published Apr 8, 2020 · Updated Aug 5, 2024

Information disclosure in Varnish Cache allows remote attackers to read stale connection workspace data through a crafted request sequence. The cnt_recv_prep function fails to reset req->err_code and req->err_reason, allowing synthetic handling to place a prior request's error reason in the HTTP response. Exploitation requires request reuse on one connection and an internal-error path, such as exhausted restarts, invalid backend headers, or an invalid VCL switch; disclosure is limited to workspace data from that connection.

CVSS severity7.5
High
EPSS probability1.79%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in Varnish Cache allows remote attackers to read stale connection workspace data through a crafted request sequence. The cnt_recv_prep function fails to reset req->err_code and req->err_reason, allowing synthetic handling to place a prior request's error reason in the HTTP response. Exploitation requires request reuse on one connection and an internal-error path, such as exhausted restarts, invalid backend headers, or an invalid VCL switch; disclosure is limited to workspace data from that connection.

The record

CVE
CVE-2019-20637
Published
Apr 8, 2020
Updated
Aug 5, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-212, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 8, 2020CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
5.0NIST NVDAV:N/AC:L/Au:N/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-212Improper Removal of Sensitive Information Before Storage or Transfer
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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