CVE-2025-53538: 
Suricata vulnerability analysis and mitigation

CVE-2025-53538 is a resource starvation vulnerability in Suricata, the open-source network IDS, IPS, and NSM engine developed by OISF. The flaw involves mishandling of data on HTTP/2 stream 0, which can lead to uncontrolled memory usage and loss of network visibility. Affected versions include Suricata 7.0.10 and below, and 8.0.0-beta1 through 8.0.0-rc1. It was published on July 22, 2025, and carries a CVSS v3.1 base score of 7.5 (High) (GitHub Advisory, Red Hat Bugzilla).

The root cause is classified as CWE-400 (Uncontrolled Resource Consumption) and CWE-770 (Allocation of Resources Without Limits or Throttling). In HTTP/2, stream 0 is reserved for connection control messages; RFC 9113 section 6.1 explicitly states that receiving a DATA frame with stream identifier 0x00 must result in a connection error of type PROTOCOL_ERROR. Suricata's HTTP/2 parser failed to enforce this constraint — instead, it would open a file handle for the transaction, not close it, and set the transaction state to completed, causing unbounded memory accumulation. The fix, applied in commits 1d6d331 and 7fa88ea, adds an explicit check to forbid DATA frames on stream 0 and prevents global transactions (stream ID 0) from being assigned file flags (GitHub Commit 1, GitHub Commit 2).

Successful exploitation causes uncontrolled memory consumption in the Suricata process, ultimately leading to loss of network visibility — meaning the IDS/IPS engine can no longer inspect or alert on network traffic. There is no confidentiality or integrity impact; the sole consequence is a high availability impact against the Suricata monitoring service itself. In environments relying on Suricata for intrusion detection or prevention, exploitation could allow malicious traffic to pass undetected during the period of resource exhaustion (GitHub Advisory).

No public proof-of-concept exploit code is known to exist, and there is no evidence of in-the-wild exploitation at this time. The vulnerability is remotely exploitable with no authentication or user interaction required (network-accessible, low complexity), making it straightforward to trigger by sending crafted HTTP/2 DATA frames targeting stream 0. The EPSS score is approximately 0.038%, indicating a low current probability of exploitation in the wild. CVE-2025-53538 is not listed in the CISA Known Exploited Vulnerabilities catalog (GitHub Advisory, Red Hat CVE).

1. Identify target: Locate a network segment monitored by a vulnerable Suricata instance (version ≤ 7.0.10 or 8.0.0-beta1/rc1) with the HTTP/2 parser enabled.
2. Craft malformed HTTP/2 traffic: Construct HTTP/2 DATA frames with the stream identifier field set to 0x00 (stream 0), which is reserved for connection control and should never carry DATA frames per RFC 9113 section 6.1.
3. Send traffic through monitored network: Transmit the crafted HTTP/2 frames across the network segment being monitored by Suricata, causing the parser to process the invalid frames.
4. Trigger resource exhaustion: Each malformed DATA frame on stream 0 causes Suricata to open a file handle for the associated transaction without properly closing it, leading to progressive memory accumulation.
5. Achieve loss of visibility: Sustain the stream of malformed frames until Suricata's memory is exhausted, causing the engine to become unresponsive or crash, eliminating network security monitoring for the duration of the attack (GitHub Advisory, GitHub Commit 1).

• Network: Unusual HTTP/2 traffic containing DATA frames with stream identifier 0x00 (stream 0); repeated or sustained HTTP/2 connections sending protocol-violating frames.
• Process: Suricata process exhibiting abnormally high and growing memory consumption; Suricata becoming unresponsive or crashing unexpectedly.
• Logs: Suricata alert logs triggering the new event http2.data_stream_zero (added in the fix); absence of expected IDS/IPS alerts during periods of high HTTP/2 traffic may indicate engine failure.
• System: Out-of-memory (OOM) killer events in system logs (/var/log/syslog, dmesg) referencing the Suricata process; unexpected Suricata service restarts (GitHub Commit 1).

Upgrade Suricata to version 7.0.11 or 8.0.0, which contain the fix (GitHub Advisory). If immediate patching is not possible, two workarounds are available: (1) disable the HTTP/2 parser entirely in the Suricata configuration, or (2) add the following Suricata signature to drop the malicious traffic: drop http2 any any -> any any (frame:http2.hdr; byte_test:1,=,0,3; byte_test:4,=,0,5; sid: 1;) — where the first byte_test matches the HTTP/2 DATA frame type and the second matches stream ID 0. Fedora and Debian have also issued updated packages for their respective distributions (Red Hat Bugzilla).

The Suricata project released version 7.0.11 on July 8, 2025, ahead of the formal CVE publication on July 22, 2025, indicating coordinated disclosure. Red Hat tracked the issue via Bugzilla and assessed it as medium severity for their products. No significant broader media coverage or notable researcher commentary beyond the official advisory has been identified.