CVE-2026-92392: curl HTTP/2 Use After Free Vulnerability

CVE-2026-92392 Overview

CVE-2026-92392 is a use-after-free vulnerability in curl's HTTP/2 upload handling. During an upload, curl mishandles an HTTP/2 RST_STREAM frame received from the server when the reason code is HTTP_1_1_REQUIRED or REFUSED_STREAM. The flaw leads to a use-after-free of a struct Curl_easy object, which can cause memory corruption or crashes in client applications that rely on libcurl for HTTP/2 transfers.

Critical Impact
A malicious or compromised HTTP/2 server can trigger memory corruption in curl clients performing uploads by returning specific RST_STREAM reason codes, potentially causing denial of service or further exploitation.

Affected Products

curl / libcurl (HTTP/2 upload code path)
Applications linking against vulnerable libcurl builds with HTTP/2 support enabled
Systems using curl as an upload client to HTTP/2 endpoints

Discovery Timeline

2026-10-14 - CVE-2026-92392 published to the National Vulnerability Database (NVD)
2026-10-14 - Last updated in NVD database
Additional details available in the curl.se CVE-2026-92392 advisory and HackerOne Report #4030333

Technical Details for CVE-2026-92392

Vulnerability Analysis

The vulnerability occurs in the HTTP/2 upload code path within libcurl. When a server returns an RST_STREAM frame with the reason HTTP_1_1_REQUIRED or REFUSED_STREAM, curl's internal retry and cleanup logic releases the associated struct Curl_easy transfer handle while references to the object are still live. Subsequent access to the freed object constitutes a use-after-free condition [CWE-416].

The HTTP_1_1_REQUIRED code instructs the client to downgrade to HTTP/1.1 and retry the request, while REFUSED_STREAM signals that the server never processed the stream and the client may retry on a new connection. Both paths involve state transitions that free and re-create transfer state, which is where the lifecycle bug manifests.

Root Cause

The root cause is incorrect object-lifetime management during error recovery in the HTTP/2 upload path. The struct Curl_easy handle is freed in response to the stream reset before all references held by the HTTP/2 session and upload machinery are cleared. When the freed memory is later dereferenced, behavior becomes undefined.

Attack Vector

Exploitation requires a server-controlled HTTP/2 endpoint that curl uploads data to. An attacker operating a malicious server, or a network attacker who can intercept and respond to an HTTP/2 upload, sends a crafted RST_STREAM frame with HTTP_1_1_REQUIRED or REFUSED_STREAM. The curl client then triggers the use-after-free during its retry handling. See the curl.se advisory for exploitation prerequisites.

Refer to the HackerOne Report #4030333 and the curl.se JSON metadata for additional technical context. No public proof-of-concept exploit is referenced in the advisory data.

Detection Methods for CVE-2026-92392

Indicators of Compromise

Unexpected crashes or segmentation faults in processes using libcurl during HTTP/2 uploads
Repeated RST_STREAM frames with reason code HTTP_1_1_REQUIRED (0x0d) or REFUSED_STREAM (0x07) observed in outbound HTTP/2 traffic
Memory corruption signatures reported by AddressSanitizer or system crash dumps referencing Curl_easy structures

Detection Strategies

Inventory all binaries statically or dynamically linked against libcurl and identify versions affected per the curl.se advisory
Instrument curl-based upload workloads with sanitizers in test environments to surface use-after-free conditions
Inspect HTTP/2 traffic from managed clients for anomalous server-sent RST_STREAM frames with the specific reason codes during upload flows

Monitoring Recommendations

Monitor process crash telemetry and core dumps for applications performing outbound HTTP/2 transfers
Alert on repeated TLS or HTTP/2 session resets originating from untrusted upstream endpoints
Track outbound HTTP/2 destinations used by CI/CD, backup, and telemetry tools that rely on curl for uploads

How to Mitigate CVE-2026-92392

Immediate Actions Required

Review the curl.se CVE-2026-92392 advisory to identify the affected and fixed curl versions in your environment
Upgrade curl and libcurl to the patched release across endpoints, servers, containers, and application dependencies
Rebuild and redeploy applications that statically link libcurl once the fixed version is available

Patch Information

The curl project maintains the authoritative patch and version metadata for this issue. Consult the curl.se CVE-2026-92392 documentation and the accompanying JSON details for the specific fixed version and commit references. Operating system vendors typically backport curl fixes to supported distribution packages.

Workarounds

Force curl to use HTTP/1.1 for uploads by passing --http1.1 on the command line or setting CURLOPT_HTTP_VERSION to CURL_HTTP_VERSION_1_1 in libcurl applications
Restrict uploads to trusted HTTP/2 endpoints under organizational control until patching completes
Disable HTTP/2 support at build time where feasible for applications that do not require it

bash

# Workaround: force HTTP/1.1 for curl uploads
curl --http1.1 -T payload.bin https://upload.example.com/path

# libcurl equivalent (C):
# curl_easy_setopt(handle, CURLOPT_HTTP_VERSION, CURL_HTTP_VERSION_1_1);