7.5

CVE-2026-9545: exposing HTTP/3 early data

Modified
AliasesALPINE-CVE-2026-9545UBUNTU-CVE-2026-9545DEBIAN-CVE-2026-9545
Published 03-07-2026Last modified 15-09-2026

Vulnerability summary

CVE-2026-9545 is a high (CVSS 7.5) vulnerability in curl. EPSS estimates a 0.41% chance of exploitation in the next 30 days, higher than 35.1% of scored vulnerabilities. 1 public exploit is recorded.

Priority
Prioritisepublic exploit

Public exploit (reference, Date unknown)

Source freshness unavailable

How is this decided?
CVSS score
7.5/10
010
High · v3.1 (CVE.org)
EPSS score
0.41%
0%100%
Low · 0.00 pp in 30 days
KEVNot listedNot listed by any tracked catalog.
RansomwareNot flaggedNo ransomware use recorded.
Public exploits1reference

Advisory lineage

Upstream 0 · Downstream 10 · Related 11
OPENSUSE-SU-2026:11230-1OPENSUSE-SU-2026:21272-1RHSA-2026:41240SUSE-SU-2026:22553-1SUSE-SU-2026:22582-1SUSE-SU-2026:22709-1

Timeline

  1. 03-07-2026
    PublishedVulnerability first disclosed.
  2. 15-09-2026
    Last modifiedVulnerability information updated.

Description

In this scenario, libcurl first uses a proper HTTP/3 server for the initial transfers, and when it makes a second transfer to the same site it has been replaced by the attacker's impostor machine - without a valid certificate. When libcurl returns to the hostname the second time with a cached SSL session (`CURLOPT_SSL_SESSIONID_CACHE` is not disabled) and early data enabled (the `CURLSSLOPT_EARLYDATA` bit is set in `CURLOPT_SSL_OPTIONS`), libcurl might send off the second request's bytes on that new connection *before* enforcing the certificate verification failure. Potentially leaking sensitive information.

CVSS metrics

6 scores · 6 sources · 1 version

EPSS trend

Probability

0.41%

Chance of exploitation in the next 30 days

Percentile

35%

Versus all other CVEs

30-day change

No change 0.00 pp

From 0.41% on 04-10-2026

04-10-202603-11-2026

Known exploited

Compare KEV catalogs
CISA KEV

Not in the CISA KEV catalog.

ENISA CNW

Not in the ENISA CNW catalog.

CIRCL

Not in the CIRCL catalog.

Public exploits

1 found
  • referenceUnverified

    Exploit Reference (hackerone.com)

    Maturity: unknown

Weaknesses

CWE · root cause

Affected systems

Version check

Known conditions: network-reachable, no authentication, no user interaction (CVSS vector). Other conditions: not stated in public data.

Chainguard10 products
  • eco-python-curl< 8.21.0-r0
  • eco-python-curl-minimal< 8.21.0-r0
  • eco-python-curl-minimal-bin< 8.21.0-r0
  • eco-python-curl-minimal-dev< 8.21.0-r0
  • eco-python-curl-minimal-doc< 8.21.0-r0
Alpine1 product
  • curl≥ 8.11.0, < 8.22.0-r0 | ≥ 8.11.0, < 8.21.0-r0
Curl1 product
  • curl≥ 8.11.0, < 8.14.2 | ≥ 8.15.0, < 8.16.1 | ≥ 8.17.0, < 8.20.1 | ≥ 962097b8dd44ed5b9e7984bc1cdffdbdd566857f, < 7b9613fa9b1a5e04301a3920eef58e8138dad05e | 8.20.0 | 8.19.0 | 8.18.0 | 8.17.0 | 8.16.0 | 8.15.0 | 8.14.1 | 8.14.0 | 8.13.0 | 8.12.1 | 8.12.0 | 8.11.1 | 8.11.0
Debian1 product
  • curlAll versions (No fix recorded) | < 8.21.0~rc2-1
Haxx1 product
  • curl≥ 8.11.0, < 8.21.0
Ubuntu1 product
  • curl< 8.14.1-2ubuntu1.4 | < 8.18.0-1ubuntu2.2

6 vendors · 15 products

References

11 links
Show all 11 references