OTP: Inconsistent Interpretation of HTTP Requests
CVE-2026-23941 is a critical-severity inconsistent interpretation of HTTP requests vulnerability in OTP from Erlang, with a CVSS 3.1 base score of 9.4 out of 10. It can be exploited remotely over the network by an unauthenticated attacker, without any action from a user. Affected OTP versions: 17.0 and later; 5.10 and later; 84adefa331c4159d432d22840663c38f155cd4c1 and later. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.51% chance of exploitation within 30 days, which is low compared with other CVEs.
Critical severity: a successful attack would have severe impact.
What to do
- Update Erlang/inets to 9.1.0.5 or 9.3.2.3 or 9.6.1, whichever matches your release line, or a later version.
- Update Erlang/otp to 26.2.5.18 or 27.3.4.9 or 28.4.1, whichever matches your release line, or a later version.
- Read the advisory on cna.erlef.org for workarounds and exact fixed builds.
- Until you can update, restrict network access to the affected service so it is not reachable from untrusted networks.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Erlang | OTP | 17.0 and later; 5.10 and later; 84adefa331c4159d432d22840663c38f155cd4c1 and later | Not stated |
| Erlang | Erlang/inets | 5.10 up to, but not including, 9.1.0.5; 9.3 up to, but not including, 9.3.2.3; 9.6 up to, but not including, 9.6.1 | 9.1.0.5, 9.3.2.3, 9.6.1 |
| Erlang | Erlang/otp | 17.0 up to, but not including, 26.2.5.18; 27.0 up to, but not including, 27.3.4.9; 28.0 up to, but not including, 28.4.1 | 26.2.5.18, 27.3.4.9, 28.4.1 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- NoneNo account or login is needed.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- LowPerformance or availability is reduced.
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:L. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 7.0 | High | CNA |
| CVSS 3.1 | 9.4 | Critical | NVD |
Official description
Inconsistent Interpretation of HTTP Requests ('HTTP Request Smuggling') vulnerability in Erlang OTP (inets httpd module) allows HTTP Request Smuggling. This vulnerability is associated with program files lib/inets/src/http_server/httpd_request.erl and program routines httpd_request:parse_headers/7. The server does not reject or normalize duplicate Content-Length headers. The earliest Content-Length in the request is used for body parsing while common reverse proxies (nginx, Apache httpd, Envoy) honor the last Content-Length value. This violates RFC 9112 Section 6.3 and allows front-end/back-end desynchronization, leaving attacker-controlled bytes queued as the start of the next request. This issue affects OTP from OTP 17.0 before OTP 26.2.5.18, OTP 27.3.4.9, and OTP 28.4.1, corresponding to inets from 5.10 before 9.1.0.5, 9.3.2.3, and 9.6.1. Whether OTP before OTP 17.0, corresponding to inets before 5.10, is affected is unknown.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Inconsistent Interpretation of HTTP Requests
The product acts as an intermediary HTTP agent (such as a proxy or firewall) in the data flow between two entities such as a client and server, but it does not interpret malformed HTTP requests or responses in ways that are consistent with how the messages will be processed by those entities that are at the ultimate destination.
How developers prevent this class of flaw
- Use a web server that employs a strict HTTP parsing procedure, such as Apache.
- Terminate the client session after each request.
More Inconsistent Interpretation of HTTP Requests vulnerabilities (CWE-444)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
Third-party and government advisories
- osv.dev/vulnerability/EEF-CVE-2026-23941Third Party Advisory
Other references
Other vulnerabilities in OTP
- 8.2 High severity
- 9.3 Critical severity
- 7.1 High severity
- 8.2 High severity
- 8.2 High severity
- 8.7 High severity
Recent Inconsistent Interpretation of HTTP Requests vulnerabilities
- 9.8 Critical severity
- 9.1 Critical severity
- 9.1 Critical severity
- 9.8 Critical severity
- 8.2 High severity
- 7.5 High severity
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