Apache Traffic Server: Request smuggling via reused origin connection
Summary
Apache Traffic Server (ATS), a caching forward and reverse proxy, can return an origin connection to its pool while the origin still waits for a request body that the client declared but did not fully send, including with Expect: 100-continue. The origin then reads the next request on that connection as leftover body data. A remote, unauthenticated attacker can exploit this to smuggle requests past ATS access controls, disrupt other users' requests, or poison the cache. The vendor rates the issue important (CVSS 4.0 9.1, critical in the input data).
Affected
- Apache Traffic Server 8.0.0 through 8.1.11
- Apache Traffic Server 9.0.0 through 9.2.15
- Apache Traffic Server 10.0.0 through 10.1.4
- Apache Traffic Server 10.2.0
Fixed in
- 9.2.x: fixed in 9.2.16
- 10.1.x: fixed in 10.1.5
- 10.2.x: fixed in 10.2.1
- 8.x: Unknown. No fixed 8.x release was found; treat 8.x as end-of-life.
Workaround
Unknown. No vendor-documented workaround was found; patching is the stated remedy.
Exploitation
- Not known to be exploited in the wild; not listed in CISA KEV at the time of research.
- CISA SSVC: exploitation none, automatable no, technical impact total.
- No public proof of concept found; EPSS is below 1%.
Our recommendation
- Identify all Apache Traffic Server instances, including those bundled in other products.
- Upgrade to 9.2.16, 10.1.5 or 10.2.1, depending on the branch in use.
- Plan a migration off any 8.x deployment, as no fixed 8.x release is known.
- Apply the same release, which also fixes related request-smuggling issues such as CVE-2026-111809.
- Monitor proxy and origin logs for malformed requests and unexpected cache content until patched.
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Apache Traffic Server mailing list announcement lists.apache.org
- Apache Traffic Server security advisory 2026-10 trafficserver.apache.org
- Ubuntu security notice CVE-2025-31699 ubuntu.com
- VulDB entry 424946 vuldb.com
- Rescana: ATS security release October 2026 www.rescana.com
- OpenCVE CVE-2025-31699 app.opencve.io
- Vulners Rapid7 CVE-2025-31699 vulners.com
- Strix CVE-2025-31699 www.strix.ai
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 31 Oct 2026, 05:35.
Original description (NVD)
Apache Traffic Server can return an origin connection to the shared pool while the origin is still waiting on a request body the client declared but never fully sent, including when the client used Expect: 100-continue. The origin then reads a later request on that connection as leftover body data, which lets an attacker smuggle requests past ATS access controls, disrupt other users' requests, or poison the cache. This issue affects Apache Traffic Server: from 8.0.0 through 8.1.11, from 9.0.0 through 9.2.15, from 10.0.0 through 10.1.4, 10.2.0. Users are recommended to upgrade to version 9.2.16, 10.1.5, or 10.2.1, which fix the issue.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
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