CVE-2026-4873Network attack vector

Cleartext disclosure via STARTTLS connection reuse

Published May 13, 2026 · Updated May 13, 2026

Cleartext transmission in curl 7.20.0 through 8.19.0 allows remote attackers to read STARTTLS session data over the network. The connection matcher in lib/url.c omits the new transfer's CURLUSESSL_CONTROL requirement, so it accepts a pooled cleartext connection. Triggering requires sequential IMAP, POP3, or SMTP transfers to the same host with the same credentials and scheme; the first is cleartext and the second requires TLS.

CVSS severity5.9
Medium
EPSS probability0.33%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Cleartext transmission in curl 7.20.0 through 8.19.0 allows remote attackers to read STARTTLS session data over the network. The connection matcher in lib/url.c omits the new transfer's CURLUSESSL_CONTROL requirement, so it accepts a pooled cleartext connection. Triggering requires sequential IMAP, POP3, or SMTP transfers to the same host with the same credentials and scheme; the first is cleartext and the second requires TLS.

The record

CVE
CVE-2026-4873
Published
May 13, 2026
Updated
May 13, 2026
Vendor
curl
Product
curl
Classifications
CWE-319, T1040
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 13, 2026CVE publishedPublication date reported by the CVE source.
  2. May 13, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=7.20.0 <=7.20.0
  2. Affected versionversion=7.20.1 <=7.20.1
  3. Affected versionversion=7.21.0 <=7.21.0
  4. Affected versionversion=7.21.1 <=7.21.1
  5. Affected versionversion=7.21.2 <=7.21.2
  6. Affected versionversion=7.21.3 <=7.21.3
  7. Affected versionversion=7.21.4 <=7.21.4
  8. Affected versionversion=7.21.5 <=7.21.5
  9. Affected versionversion=7.21.6 <=7.21.6
  10. Affected versionversion=7.21.7 <=7.21.7
  11. Affected versionversion=7.22.0 <=7.22.0
  12. Affected versionversion=7.23.0 <=7.23.0
  13. Affected versionversion=7.23.1 <=7.23.1
  14. Affected versionversion=7.24.0 <=7.24.0
  15. Affected versionversion=7.25.0 <=7.25.0
  16. Affected versionversion=7.26.0 <=7.26.0
  17. Affected versionversion=7.27.0 <=7.27.0
  18. Affected versionversion=7.28.0 <=7.28.0
  19. Affected versionversion=7.28.1 <=7.28.1
  20. Affected versionversion=7.29.0 <=7.29.0
  21. Affected versionversion=7.30.0 <=7.30.0
  22. Affected versionversion=7.31.0 <=7.31.0
  23. Affected versionversion=7.32.0 <=7.32.0
  24. Affected versionversion=7.33.0 <=7.33.0
  25. Affected versionversion=7.34.0 <=7.34.0
  26. Affected versionversion=7.35.0 <=7.35.0
  27. Affected versionversion=7.36.0 <=7.36.0
  28. Affected versionversion=7.37.0 <=7.37.0
  29. Affected versionversion=7.37.1 <=7.37.1
  30. Affected versionversion=7.38.0 <=7.38.0
  31. Affected versionversion=7.39.0 <=7.39.0
  32. Affected versionversion=7.40.0 <=7.40.0
  33. Affected versionversion=7.41.0 <=7.41.0
  34. Affected versionversion=7.42.0 <=7.42.0
  35. Affected versionversion=7.42.1 <=7.42.1
  36. Affected versionversion=7.43.0 <=7.43.0
  37. Affected versionversion=7.44.0 <=7.44.0
  38. Affected versionversion=7.45.0 <=7.45.0
  39. Affected versionversion=7.46.0 <=7.46.0
  40. Affected versionversion=7.47.0 <=7.47.0
  41. Affected versionversion=7.47.1 <=7.47.1
  42. Affected versionversion=7.48.0 <=7.48.0
  43. Affected versionversion=7.49.0 <=7.49.0
  44. Affected versionversion=7.49.1 <=7.49.1
  45. Affected versionversion=7.50.0 <=7.50.0
  46. Affected versionversion=7.50.1 <=7.50.1
  47. Affected versionversion=7.50.2 <=7.50.2
  48. Affected versionversion=7.50.3 <=7.50.3
  49. Affected versionversion=7.51.0 <=7.51.0
  50. Affected versionversion=7.52.0 <=7.52.0
  51. Affected versionversion=7.52.1 <=7.52.1
  52. Affected versionversion=7.53.0 <=7.53.0
  53. Affected versionversion=7.53.1 <=7.53.1
  54. Affected versionversion=7.54.0 <=7.54.0
  55. Affected versionversion=7.54.1 <=7.54.1
  56. Affected versionversion=7.55.0 <=7.55.0
  57. Affected versionversion=7.55.1 <=7.55.1
  58. Affected versionversion=7.56.0 <=7.56.0
  59. Affected versionversion=7.56.1 <=7.56.1
  60. Affected versionversion=7.57.0 <=7.57.0
  61. Affected versionversion=7.58.0 <=7.58.0
  62. Affected versionversion=7.59.0 <=7.59.0
  63. Affected versionversion=7.60.0 <=7.60.0
  64. Affected versionversion=7.61.0 <=7.61.0
  65. Affected versionversion=7.61.1 <=7.61.1
  66. Affected versionversion=7.62.0 <=7.62.0
  67. Affected versionversion=7.63.0 <=7.63.0
  68. Affected versionversion=7.64.0 <=7.64.0
  69. Affected versionversion=7.64.1 <=7.64.1
  70. Affected versionversion=7.65.0 <=7.65.0
  71. Affected versionversion=7.65.1 <=7.65.1
  72. Affected versionversion=7.65.2 <=7.65.2
  73. Affected versionversion=7.65.3 <=7.65.3
  74. Affected versionversion=7.66.0 <=7.66.0
  75. Affected versionversion=7.67.0 <=7.67.0
  76. Affected versionversion=7.68.0 <=7.68.0
  77. Affected versionversion=7.69.0 <=7.69.0
  78. Affected versionversion=7.69.1 <=7.69.1
  79. Affected versionversion=7.70.0 <=7.70.0
  80. Affected versionversion=7.71.0 <=7.71.0
  81. Affected versionversion=7.71.1 <=7.71.1
  82. Affected versionversion=7.72.0 <=7.72.0
  83. Affected versionversion=7.73.0 <=7.73.0
  84. Affected versionversion=7.74.0 <=7.74.0
  85. Affected versionversion=7.75.0 <=7.75.0
  86. Affected versionversion=7.76.0 <=7.76.0
  87. Affected versionversion=7.76.1 <=7.76.1
  88. Affected versionversion=7.77.0 <=7.77.0
  89. Affected versionversion=7.78.0 <=7.78.0
  90. Affected versionversion=7.79.0 <=7.79.0
  91. Affected versionversion=7.79.1 <=7.79.1
  92. Affected versionversion=7.80.0 <=7.80.0
  93. Affected versionversion=7.81.0 <=7.81.0
  94. Affected versionversion=7.82.0 <=7.82.0
  95. Affected versionversion=7.83.0 <=7.83.0
  96. Affected versionversion=7.83.1 <=7.83.1
  97. Affected versionversion=7.84.0 <=7.84.0
  98. Affected versionversion=7.85.0 <=7.85.0
  99. Affected versionversion=7.86.0 <=7.86.0
  100. Affected versionversion=7.87.0 <=7.87.0
  101. Affected versionversion=7.88.0 <=7.88.0
  102. Affected versionversion=7.88.1 <=7.88.1
  103. Affected versionversion=8.0.0 <=8.0.0
  104. Affected versionversion=8.0.1 <=8.0.1
  105. Affected versionversion=8.10.0 <=8.10.0
  106. Affected versionversion=8.10.1 <=8.10.1
  107. Affected versionversion=8.1.0 <=8.1.0
  108. Affected versionversion=8.11.0 <=8.11.0
  109. Affected versionversion=8.11.1 <=8.11.1
  110. Affected versionversion=8.1.1 <=8.1.1
  111. Affected versionversion=8.12.0 <=8.12.0
  112. Affected versionversion=8.12.1 <=8.12.1
  113. Affected versionversion=8.1.2 <=8.1.2
  114. Affected versionversion=8.13.0 <=8.13.0
  115. Affected versionversion=8.14.0 <=8.14.0
  116. Affected versionversion=8.14.1 <=8.14.1
  117. Affected versionversion=8.15.0 <=8.15.0
  118. Affected versionversion=8.16.0 <=8.16.0
  119. Affected versionversion=8.17.0 <=8.17.0
  120. Affected versionversion=8.18.0 <=8.18.0
  121. Affected versionversion=8.19.0 <=8.19.0
  122. Affected versionversion=8.2.0 <=8.2.0
  123. Affected versionversion=8.2.1 <=8.2.1
  124. Affected versionversion=8.3.0 <=8.3.0
  125. Affected versionversion=8.4.0 <=8.4.0
  126. Affected versionversion=8.5.0 <=8.5.0
  127. Affected versionversion=8.6.0 <=8.6.0
  128. Affected versionversion=8.7.0 <=8.7.0
  129. Affected versionversion=8.7.1 <=8.7.1
  130. Affected versionversion=8.8.0 <=8.8.0
  131. Affected versionversion=8.9.0 <=8.9.0
  132. Affected versionversion=8.9.1 <=8.9.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

curl · curlversion=7.20.0 <=7.20.0; version=7.20.1 <=7.20.1; version=7.21.0 <=7.21.0; version=7.21.1 <=7.21.1; version=7.21.2 <=7.21.2; version=7.21.3 <=7.21.3; version=7.21.4 <=7.21.4; version=7.21.5 <=7.21.5; version=7.21.6 <=7.21.6; version=7.21.7 <=7.21.7; version=7.22.0 <=7.22.0; version=7.23.0 <=7.23.0; version=7.23.1 <=7.23.1; version=7.24.0 <=7.24.0; version=7.25.0 <=7.25.0; version=7.26.0 <=7.26.0; version=7.27.0 <=7.27.0; version=7.28.0 <=7.28.0; version=7.28.1 <=7.28.1; version=7.29.0 <=7.29.0; version=7.30.0 <=7.30.0; version=7.31.0 <=7.31.0; version=7.32.0 <=7.32.0; version=7.33.0 <=7.33.0; version=7.34.0 <=7.34.0; version=7.35.0 <=7.35.0; version=7.36.0 <=7.36.0; version=7.37.0 <=7.37.0; version=7.37.1 <=7.37.1; version=7.38.0 <=7.38.0; version=7.39.0 <=7.39.0; version=7.40.0 <=7.40.0; version=7.41.0 <=7.41.0; version=7.42.0 <=7.42.0; version=7.42.1 <=7.42.1; version=7.43.0 <=7.43.0; version=7.44.0 <=7.44.0; version=7.45.0 <=7.45.0; version=7.46.0 <=7.46.0; version=7.47.0 <=7.47.0; version=7.47.1 <=7.47.1; version=7.48.0 <=7.48.0; version=7.49.0 <=7.49.0; version=7.49.1 <=7.49.1; version=7.50.0 <=7.50.0; version=7.50.1 <=7.50.1; version=7.50.2 <=7.50.2; version=7.50.3 <=7.50.3; version=7.51.0 <=7.51.0; version=7.52.0 <=7.52.0; version=7.52.1 <=7.52.1; version=7.53.0 <=7.53.0; version=7.53.1 <=7.53.1; version=7.54.0 <=7.54.0; version=7.54.1 <=7.54.1; version=7.55.0 <=7.55.0; version=7.55.1 <=7.55.1; version=7.56.0 <=7.56.0; version=7.56.1 <=7.56.1; version=7.57.0 <=7.57.0; version=7.58.0 <=7.58.0; version=7.59.0 <=7.59.0; version=7.60.0 <=7.60.0; version=7.61.0 <=7.61.0; version=7.61.1 <=7.61.1; version=7.62.0 <=7.62.0; version=7.63.0 <=7.63.0; version=7.64.0 <=7.64.0; version=7.64.1 <=7.64.1; version=7.65.0 <=7.65.0; version=7.65.1 <=7.65.1; version=7.65.2 <=7.65.2; version=7.65.3 <=7.65.3; version=7.66.0 <=7.66.0; version=7.67.0 <=7.67.0; version=7.68.0 <=7.68.0; version=7.69.0 <=7.69.0; version=7.69.1 <=7.69.1; version=7.70.0 <=7.70.0; version=7.71.0 <=7.71.0; version=7.71.1 <=7.71.1; version=7.72.0 <=7.72.0; version=7.73.0 <=7.73.0; version=7.74.0 <=7.74.0; version=7.75.0 <=7.75.0; version=7.76.0 <=7.76.0; version=7.76.1 <=7.76.1; version=7.77.0 <=7.77.0; version=7.78.0 <=7.78.0; version=7.79.0 <=7.79.0; version=7.79.1 <=7.79.1; version=7.80.0 <=7.80.0; version=7.81.0 <=7.81.0; version=7.82.0 <=7.82.0; version=7.83.0 <=7.83.0; version=7.83.1 <=7.83.1; version=7.84.0 <=7.84.0; version=7.85.0 <=7.85.0; version=7.86.0 <=7.86.0; version=7.87.0 <=7.87.0; version=7.88.0 <=7.88.0; version=7.88.1 <=7.88.1; version=8.0.0 <=8.0.0; version=8.0.1 <=8.0.1; version=8.10.0 <=8.10.0; version=8.10.1 <=8.10.1; version=8.1.0 <=8.1.0; version=8.11.0 <=8.11.0; version=8.11.1 <=8.11.1; version=8.1.1 <=8.1.1; version=8.12.0 <=8.12.0; version=8.12.1 <=8.12.1; version=8.1.2 <=8.1.2; 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=8.2.0 <=8.2.0; version=8.2.1 <=8.2.1; version=8.3.0 <=8.3.0; version=8.4.0 <=8.4.0; version=8.5.0 <=8.5.0; version=8.6.0 <=8.6.0; version=8.7.0 <=8.7.0; version=8.7.1 <=8.7.1; version=8.8.0 <=8.8.0; version=8.9.0 <=8.9.0; version=8.9.1 <=8.9.1

Published CVSS scores

5.9CISA-ADPCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-319Cleartext Transmission of Sensitive Information
T1040Network Sniffing

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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