curl: Insertion of Sensitive Information Into Sent Data
CVE-2026-86409 is a high-severity insertion of sensitive information into sent data vulnerability in curl, with a CVSS 3.1 base score of 8.1 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected curl versions: 8.21.0 and earlier; 8.20.0 and earlier; 8.19.0 and earlier, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 1.1% chance of exploitation within 30 days, higher than 66% of scored CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of curl you run against the affected versions below, and install the vendor's latest release.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Curl | curl | 8.21.0 and earlier; 8.20.0 and earlier; 8.19.0 and earlier; 8.18.0 and earlier; 8.17.0 and earlier; 8.16.0 and earlier; 8.15.0 and earlier; 8.14.1 and earlier; and 32 more ranges | Not stated |
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
- HighSuccess depends on conditions outside the attacker's control.
- 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
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).
Official description
Setting `CURLOPT_AWS_SIGV4` to NULL but does not disable SigV4 authentication, contrary to expectations and documentation. A subsequent transfer on the same handle still sends an `Authorization: AWS4-HMAC-SHA256` header to whatever URL isset next, leaking state information.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Insertion of Sensitive Information Into Sent Data
The code transmits data to another actor, but a portion of the data includes sensitive information that should not be accessible to that actor.
How developers prevent this class of flaw
- Specify which data in the software should be regarded as sensitive. Consider which types of users should have access to which types of data.
- Ensure that any possibly sensitive data specified in the requirements is verified with designers to ensure that it is either a calculated risk or mitigated elsewhere. Any information that is not necessary to the functionality should be removed in order to lower both the overhead and the possibility of security sensitive data being sent.
- Setup default error messages so that unexpected errors do not disclose sensitive information.
More Insertion of Sensitive Information Into Sent Data vulnerabilities (CWE-201)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Other references
Other vulnerabilities in curl
- 7.5 High severity
- 9.1 Critical severity
- 7.5 High severity
- 7.5 High severity
- 8.1 High severity
- 9.1 Critical severity
Recent Insertion of Sensitive Information Into Sent Data vulnerabilities
- 8.1 High severity
- 8.1 High severity
- 9.1 Critical severity
- 7.5 High severity
- 9.1 Critical severity
- 9.1 Critical severity
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