curl: Double Free
CVE-2026-8925 is a critical-severity double free vulnerability in curl, with a CVSS 3.1 base score of 9.8 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 8.16.1, 8.20.1, 3da249e1f0716c06644ed3522a37a8bf81808012 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 1.08% chance of exploitation within 30 days, higher than 66% of scored CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update curl to 8.16.1 or 8.20.1 or 3da249e1f0716c06644ed3522a37a8bf81808012, 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 | 8.15.0 up to, but not including, 8.16.1; 8.17.0 up to, but not including, 8.20.1; ab650379a8c25ca952f651476d25b4cdd77bb3fc up to, but not including, 3da249e1f0716c06644ed3522a37a8bf81808012; 8.20.0; 8.19.0; 8.18.0; 8.17.0; 8.16.0; and 1 more ranges | 8.16.1, 8.20.1, 3da249e1f0716c06644ed3522a37a8bf81808012 |
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
- 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:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by CISA (ADP).
Official description
The curl logic that works with SASL authentication could end up cleaning up the GSASL context *twice* without clearing the pointer in between, making it `free()` the same pointer twice.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Double Free
The product calls free() twice on the same memory address.
How developers prevent this class of flaw
- Choose a language that provides automatic memory management.
- Ensure that each allocation is freed only once. After freeing a chunk, set the pointer to NULL to ensure the pointer cannot be freed again. In complicated error conditions, be sure that clean-up routines respect the state of allocation properly. If the language is object oriented, ensure that object destructors delete each chunk of memory only once.
- Use a static analysis tool to find double free instances.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: poc, automatable: yes, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Technical write-ups (may include proof of concept)
- hackerone.com/reports/3735193Exploit, Issue Tracking, 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 Double Free vulnerabilities
- 7.3 High severity
- 8.1 High severity
- 7.5 High severity
- 8.8 High severity
- 7.8 High severity
- 7.8 High severity
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