CyberSecBulletin
CVE-2026-6276NVD status: Modified

curl: Cleartext Transmission of Sensitive Information

Published Updated By the CyberSecBulletin desk

CVE-2026-6276 is a high-severity cleartext transmission of sensitive information vulnerability in curl, with a CVSS 3.1 base score of 7.5 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. The record lists versions 8.14.2, 8.16.1, 8.20.0 as the first without the flaw, so updating curl to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update curl to 8.14.2 or 8.16.1 or 8.20.0 or 3a19987a87f393d9394fe5acc7643f6c263c92db, whichever matches your release line, or a later version.
  2. Read the advisory on curl.se for workarounds and exact fixed builds.
  3. Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.

Affected products and versions

VendorProductAffected versionsFixed in
Curlcurl7.71.0 up to, but not including, 8.14.2; 8.15.0 up to, but not including, 8.16.1; 8.17.0 up to, but not including, 8.20.0; e15e51384a423be31318b3c9c7d612a1aae661fd up to, but not including, 3a19987a87f393d9394fe5acc7643f6c263c92db; 8.19.0; 8.18.0; 8.17.0; 8.16.0; and 32 more ranges8.14.2, 8.16.1, 8.20.0, 3a19987a87f393d9394fe5acc7643f6c263c92db

Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
NetworkCan be exploited remotely over a network, including the internet.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
NoneNo data is disclosed.
Integrity
NoneNothing can be modified.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.5HighNVD
CVSS 3.17.5HighCISA (ADP)

Official description

Using libcurl, when a custom `Host:` header is first set for an HTTP request and a second request is subsequently done using the same *easy handle* but without the custom `Host:` header set, the second request would use stale information and pass on cookies meant for the first host in the second request. Leak them.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Cleartext Transmission of Sensitive Information

The product transmits sensitive or security-critical data in cleartext in a communication channel that can be sniffed by unauthorized actors.

How developers prevent this class of flaw

  • Before transmitting, encrypt the data using reliable, confidentiality-protecting cryptographic protocols.
  • When using web applications with SSL, use SSL for the entire session from login to logout, not just for the initial login page.
  • When designing hardware platforms, ensure that approved encryption algorithms (such as those recommended by NIST) protect paths from security critical data to trusted user applications.

More Cleartext Transmission of Sensitive Information vulnerabilities (CWE-319)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: partial).
  3. Record last changed materially (score, affected products, status or references).

References

Third-party and government advisories

Technical write-ups (may include proof of concept)

Other references

Other vulnerabilities in curl

All curl vulnerabilities

Recent Cleartext Transmission of Sensitive Information vulnerabilities

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