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How the CVE Works
CVE-2018-14717 is a critical vulnerability in Cloudflare’s reverse proxy logic. The flaw resided in the handling of HTTP/2 requests with specific, malformed header sequences. When Cloudflare processed these requests, it caused a race condition within the server’s HTTP/2 HPACK decoder. This race condition led to a state corruption, causing the Cloudflare proxy to read memory from an incorrect, already-freed buffer. The read memory content, which could contain sensitive data from previous requests processed by the same server, was then erroneously appended into the headers of an unrelated, outgoing HTTP response. This resulted in the leakage of private data, such as HTTP cookies, authentication tokens, and POST request bodies, from other user sessions to an attacker.
dailycve form:
Platform: Cloudflare WAF
Version: Pre-June 2018
Vulnerability : Memory Disclosure
Severity: Critical
date: 2018-06-19
Prediction: 2018-06-22
What Undercode Say:
curl -I --http2 https://target-site.com/ -H "X-Custom-Header: \x00"
nghttp -v -H ":method: GET" -H ":path: /" -H "custom: value1" -H "custom: value2" "https://vulnerable-site.com"
Analysis of leaked data in responses:
curl -s --http2 https://target-site.com/ | grep -oE "Cookie: [^"]+" | head -1
How Exploit:
Craft malicious HTTP/2 requests with specific header sequences to trigger the HPACK race condition. Automated tools scan for vulnerable Cloudflare endpoints. The attacker sends multiple concurrent, malformed HPACK streams. Successful exploitation causes the server to leak memory chunks containing other users’ sensitive data into the attacker’s HTTP response.
Protection from this CVE
Update Cloudflare WAF. Disable HTTP/2. Implement strict origin firewall rules. Monitor for abnormal traffic patterns.
Impact:
Widespread data leakage. Compromised user sessions. Exposure of authentication tokens. Potential account takeover.
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Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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