CVE-2026-9545Network attack vector

Request-data disclosure via deferred certificate failure

Published Jul 3, 2026 · Updated Jul 3, 2026

Information disclosure in curl and libcurl 8.11.0 through 8.20.0 allows man-in-the-middle attackers to read HTTP/3 request data. The ngtcp2 handshake-completion callback records a peer-certificate failure but continues QUIC processing, allowing cached TLS early data to be transmitted. Exposure requires the ngtcp2 and nghttp3 HTTP/3 backend, a cached TLS session, enabled early data, and an impostor endpoint replacing the original server.

CVSS severityUnavailable
Unscored
EPSS probability0.27%
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 curl and libcurl 8.11.0 through 8.20.0 allows man-in-the-middle attackers to read HTTP/3 request data. The ngtcp2 handshake-completion callback records a peer-certificate failure but continues QUIC processing, allowing cached TLS early data to be transmitted. Exposure requires the ngtcp2 and nghttp3 HTTP/3 backend, a cached TLS session, enabled early data, and an impostor endpoint replacing the original server.

The record

CVE
CVE-2026-9545
Published
Jul 3, 2026
Updated
Jul 3, 2026
Vendor
curl
Product
curl
Classifications
CWE-200, T1557
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 3, 2026CVE publishedPublication date reported by the CVE source.
  2. Jul 3, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=8.11.0 <=8.11.0
  2. Affected versionversion=8.11.1 <=8.11.1
  3. Affected versionversion=8.12.0 <=8.12.0
  4. Affected versionversion=8.12.1 <=8.12.1
  5. Affected versionversion=8.13.0 <=8.13.0
  6. Affected versionversion=8.14.0 <=8.14.0
  7. Affected versionversion=8.14.1 <=8.14.1
  8. Affected versionversion=8.15.0 <=8.15.0
  9. Affected versionversion=8.16.0 <=8.16.0
  10. Affected versionversion=8.17.0 <=8.17.0
  11. Affected versionversion=8.18.0 <=8.18.0
  12. Affected versionversion=8.19.0 <=8.19.0
  13. Affected versionversion=8.20.0 <=8.20.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=8.11.0 <=8.11.0; version=8.11.1 <=8.11.1; version=8.12.0 <=8.12.0; version=8.12.1 <=8.12.1; version=8.13.0 <=8.13.0; version=8.14.0 <=8.14.0; version=8.14.1 <=8.14.1; version=8.15.0 <=8.15.0; version=8.16.0 <=8.16.0; version=8.17.0 <=8.17.0; version=8.18.0 <=8.18.0; version=8.19.0 <=8.19.0; version=8.20.0 <=8.20.0

Published CVSS scores

No CVSS assessment is available in this record.

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-200Exposure of Sensitive Information to an Unauthorized Actor
T1557Adversary-in-the-Middle

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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