CVE-2026-124040civetweb use after free
CVE-2026-124040 is a use after free in civetweb, rated critical (9.2 on CVSS 4.0).
Why this priority: Critical, and reachable over the network without an account.
Published · Updated · NVD status: Deferred
What it is
Code keeps using memory after releasing it, so an attacker who refills that memory can steer execution.
How it is reached
An attacker can exploit it over the network, without an account, and nobody has to click anything. Success also depends on conditions the attacker does not fully control.
What an attacker gains
A successful attack can read the data it protects, change data or behaviour and take it offline. In practice, this kind of flaw lets an attacker crash the process, read memory, or in the worst case run code.
Is it being exploited?
There is no public report of exploitation yet.
What to do
- No fixed version is listed yet. Find every place civetweb runs, watch the references for a fix, and plan a replacement if it is no longer supported.
- While there is no fix, keep it off the internet or behind a VPN, allowlist or authenticating proxy.
Description from NVD
CivetWeb through 1.16, when built with USE_HTTP2 and enable_http2 on, contains a use-after-free vulnerability in handle_http2() that retains freed :method and :path pointers. Unauthenticated remote attackers can send a later HEADERS frame omitting these pseudo-headers to influence request method or path seen by access rules, or crash the server.
What this means for your architecture.
A CVE names a product. Whether it matters depends on where that product sits in your systems: what reaches it, which trust boundary it guards and what it can reach once compromised. Veriom maps your components, their relationships and your trust boundaries from your code, cloud and delivery evidence, so you can see where a component like this sits. The radar itself does not look at your systems.
Components it touches
- Native code: operating systems, browsers and firmware. The flaw sits wherever native code reads untrusted data.
- Network appliances and media or file parsers. The flaw sits wherever native code reads untrusted data.
Trust boundaries in play
- Internet-facing entry points. No account is needed. Any instance reachable from outside your perimeter, through a load balancer, gateway, VPN or exposed admin port, is in scope.
- Wherever native code reads untrusted data. An attacker who crosses it can crash the process, read memory, or in the worst case run code.
Questions to answer about your own systems
- Where does civetweb run in your systems, and at which version?
- Which of those instances can be reached from the internet or partner networks?
- What can it reach once compromised: which data stores, secrets and services?
Sources
- CVE records and CVSS scores from the NVD CVE API. This product uses the NVD API but is not endorsed or certified by the NVD.
- Exploitation status from CISA’s Known Exploited Vulnerabilities catalog.
- Exploit likelihood from FIRST’s Exploit Prediction Scoring System (EPSS), refreshed daily.
- Explanations are written by Veriom from fixed templates over each record’s data, not by a person reviewing each CVE. Descriptions are quoted from the records as published.