CAPEC-494
TCP Fragmentation
An adversary may execute a TCP Fragmentation attack against a target with the intention of avoiding filtering rules of network controls, by attempting to fragment the TCP packet such that the headers flag field is pushed into the second fragment which typically is not filtered.
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In comparison, IP fragmentation occurs when an IP datagram is larger than the MTU of the route the datagram has to traverse. This behavior of fragmentation defeats some IPS and firewall filters who typically check the FLAGS in the header of the first packet since dropping this packet prevents the following fragments from being processed and assembled.
Another variation is overlapping fragments thus that an innocuous first segment passes the filter and the second segment overwrites the TCP header data with the true payload which is malicious in nature. The malicious payload manipulated properly may lead to a DoS due to resource consumption or kernel crash. Additionally the fragmentation could be used in conjunction with sending fragments at a rate slightly slower than the timeout to cause a DoS condition by forcing resources that assemble the packet to wait an inordinate amount of time to complete the task. The fragmentation identification numbers could also be duplicated very easily as there are only 16 bits in IPv4 so only 65536 packets are needed.
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Explain the attack pattern CAPEC-494: TCP Fragmentation: how it unfolds, what it needs and how to prevent and detect it in my systems. Use https://capec.mitre.org/data/definitions/494.html and https://cve.bz/cve/capec/494?via=ask-ai-copy, which lists recent CVEs with the weaknesses it exploits. Cite the sources.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this attack pattern's id and public links.
Prerequisites
This type of an attack requires the target system to be running a vulnerable implementation of IP, and the adversary needs to ability to send TCP packets of arbitrary size with crafted data.
Mitigations
This attack may be mitigated by enforcing rules at the router following the guidance of RFC1858. The essential part of the guidance is creating the following rule "IF FO=1 and PROTOCOL=TCP then DROP PACKET" as this mitigated both tiny fragment and overlapping fragment attacks in IPv4. In IPv6 overlapping(RFC5722) additional steps may be required such as deep packet inspection. The delayed fragments may be mitigated by enforcing a timeout on the transmission to receive all packets by a certain time since the first packet is received. According to RFC2460 IPv6 implementations should enforce a rule to discard all fragments if the fragments are not ALL received within 60 seconds of the FIRST arriving fragment.
Weaknesses it exploits
- CWE-404 Improper Resource Shutdown or Release
- CWE-770 Allocation of Resources Without Limits or Throttling
Recent CVEs with these weaknesses
- –CVE-2026-86531
The embedded OpenEJB HTTP server does not limit the size of incoming request bodies or of multipart requests, and does not remove the temporary files it creates for multipart parts. A remote unauthenticated attacker can cause excessive mem…
- 7.0CVE-2026-114359
Eclipse Kura downloads deployment packages (DPs) from a remote URL without any limit on the size of the data it receives. A malicious or compromised HTTP(S) server, or an attacker able to tamper with a plain-HTTP download, can stream an ar…
- 8.7CVE-2026-60040
An unauthenticated remote attacker can perform a DoS in the backends backup creation function. This can result in a total loss of availability.
- 8.7CVE-2026-123817
AIOHTTP is an asynchronous HTTP client/server framework for asyncio and Python. Prior to 3.14.4, the WebSocket reader retains one bytes object for each transport read while reassembling an incomplete frame. A malicious peer can split a fra…
- 6.8CVE-2026-125205
FFmpeg through 9.0.2 contains an unbounded memory allocation vulnerability in the av1_frame_merge bitstream filter that allows attackers to exhaust memory by never sending a temporal delimiter OBU. Attackers can supply a crafted .obu file …
- 5.7CVE-2026-125186
FFmpeg through 9.0.2 contains an uncontrolled resource consumption vulnerability in the dts2pts bitstream filter that allows attackers to exhaust CPU through unbounded per-packet POC node allocation. Attackers can supply a crafted H.264 pa…
- 6.8CVE-2026-125180
FFmpeg 8.1 through 9.0.2 contains a memory exhaustion vulnerability in the libavcodec/exif.c parser that allows attackers to amplify allocations by pointing many IFD entries at overlapping payloads. Attackers can embed a small crafted EXIF…
- 7.5CVE-2026-112322
clean_client() in lib/rpc/svc_auth_gssapi.c in MIT Kerberos 5 (aka krb5) restarts its scan from the head of the client list after each removal, resulting in quadratic CPU cost. Remote attackers can cause a denial of service (CPU consumptio…
The newest records naming one of them. Each weakness's page lists them all.
Related attack patterns
- Part of
- CAPEC-130 Excessive Allocation
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