19 results · Feed
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High 7.5
h2o: heap exhaustion using capsules
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 4212ce114506a073505fd389db16ad2ba4e582a0, a client could send an incomplete CONNECT-UDP Capsule with an excessively large declared length, causing H2O to keep buffering receiv…
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High 8.1
h2o: buffer overflow when using the %{error}x log directive
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 48b7ae12107fd2b118e4641da49599e9aac8edd8, H2O's access-log formatter could write past its log-line buffer when an affected custom access-log format was configured. The allocat…
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High 7.5
h2o has HTTP/2 state amplification
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 9265bdd, there is an HTTP/2 state amplification issue that combines HPACK decompression amplification with Slowloris-style stream stalling. Amplified decoded header state can …
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High 7.5
h2o is vulnerable to musl libc stack overflow
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 6b5370d, h2o is vulnerable to a Denial of Service attack when calling alloca under certain conditions. When serving static files, h2o builds the file path on stack, by calling…
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Medium 5.9
h2o is vulnerable to heap overrun
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit 8dc37cb, when h2o receives a ClientHello message over TLS or QUIC and it contains a zero-length SNI extension, the h2o server runs over the zero-length hostname while trying t…
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High 7.5
h2o: musl libc stack overflow (QPACK)
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. Prior to commit edd7a120bfc4af11ac0cbebce2a43cc1f93f9af1, when h2o processes a QPACK instruction sent from the peer over HTTP/3, lib/http3/qpack.c might allocate an on-stack buffer as large a…
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High 7.5CVE-2025-8671 Public exploit
CVE-2025-8671
A mismatch caused by client-triggered server-sent stream resets between HTTP/2 specifications and the internal architectures of some HTTP/2 implementations may result in excessive server resource consumption leading to denial-of-service (DoS). By opening stre…
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Medium 5.9
H2O alllows bypassing address-based access control with 0-RTT
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. When an HTTP request using TLS/1.3 early data on top of TCP Fast Open or QUIC 0-RTT packets is received and the IP-address-based access control is used, the access control does not detect and…
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Low 3.1
H2O ignores headers configuration directives
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. The configuration directives provided by the headers handler allows users to modify the response headers being sent by h2o. The configuration file of h2o has scopes, and the inner scopes (e.g…
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Medium 6.1
h2o vulnerable to TLS session resumption misdirection
h2o is an HTTP server with support for HTTP/1.x, HTTP/2 and HTTP/3. In version 2.3.0-beta2 and prior, when h2o is configured to listen to multiple addresses or ports with each of them using different backend servers managed by multiple entities, a malicious b…
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High 7.5
HTTP/2 Stream Cancellation Attack
The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.
KEV Oct 10, 2023 -
High 7.5CVE-2019-9512 EPSS 83%
Some HTTP/2 implementations are vulnerable to ping floods, potentially leading to a denial of service
Some HTTP/2 implementations are vulnerable to ping floods, potentially leading to a denial of service. The attacker sends continual pings to an HTTP/2 peer, causing the peer to build an internal queue of responses. Depending on how efficiently this data is qu…
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High 7.5CVE-2019-9515 EPSS 87%
Some HTTP/2 implementations are vulnerable to a settings flood, potentially leading to a denial of service
Some HTTP/2 implementations are vulnerable to a settings flood, potentially leading to a denial of service. The attacker sends a stream of SETTINGS frames to the peer. Since the RFC requires that the peer reply with one acknowledgement per SETTINGS frame, an …
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High 7.5CVE-2019-9514 EPSS 83%
Some HTTP/2 implementations are vulnerable to a reset flood, potentially leading to a denial of service
Some HTTP/2 implementations are vulnerable to a reset flood, potentially leading to a denial of service. The attacker opens a number of streams and sends an invalid request over each stream that should solicit a stream of RST_STREAM frames from the peer. Depe…
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Unscored —
Buffer overflow in H2O version 2.2.4 and earlier allows remote attackers to execute arbitrary code or cause a denial of…
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Unscored —
H2O version 2.2.2 and earlier allows remote attackers to cause a denial of service in the server via specially crafted …
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Unscored —
Buffer overflow in H2O version 2.2.2 and earlier allows remote attackers to cause a denial-of-service in the server via…
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Unscored —
H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via unspecified vector…
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Unscored —
H2O version 2.2.3 and earlier allows remote attackers to cause a denial of service in the server via specially crafted …