curl: Use After Free
CVE-2026-18924 is a critical-severity use after free vulnerability in curl, with a CVSS 3.1 base score of 9.1 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, 8.20.1 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 0.58% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update curl to 8.14.2 or 8.16.1 or 8.20.1 or 8.22.0, whichever matches your release line, or a later version.
- Read the advisory on curl.se for workarounds and exact fixed builds.
- 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 | 7.44.0 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, 8.20.1; 8.21.0 up to, but not including, 8.22.0; ea7134ac874a66107e54ff93657ac565cf2ec4aa up to, but not including, 90325ff0444cbdff368bda5d26d6405a0bb6ee43; 8.21.0; 8.20.0; 8.19.0; and 32 more ranges | 8.14.2, 8.16.1, 8.20.1, 8.22.0, 90325ff0444cbdff368bda5d26d6405a0bb6ee43 |
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
- HighData or code can be modified at will.
- 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:H/A:H. Scored by CISA (ADP).
Official description
A flaw in libcurl's handling of HTTP/2 Server Push streams, when the parent handle is set to share connections with other handles, can lead to use-after-free in the cleanup process.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- When freeing pointers, be sure to set them to NULL once they are freed. However, the utilization of multiple or complex data structures may lower the usefulness of this strategy.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- hackerone.com/reports/3916059Exploit, Mitigation, Third Party Advisory
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 Use After Free vulnerabilities
- 7.5 High severity
- 7.6 High severity
- 7.8 High severity
- 8.8 High severity
- 8.3 High severity
- 9.6 Critical severity
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