CVE-2026-86146: Apache bRPC: HTTP Request Smuggling and Header Injection via Lenient HTTP/1.1 Header Parsing

Is it exploited?

Not on CISA's list. CISA has not added it to the Known Exploited Vulnerabilities catalog as of 29 Oct 2026. If CISA adds it, this page shows it as known exploited.

How likely is exploitation in the next 30 days?

0.2%

EPSS score, percentile 10.3 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

Not scored

The CVE record carries no CVSS score.

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

Advisories and patches (1)

Which versions are affected?

Affected

• before 1.18.0

Versions by product

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026; CVE List, as of 29 Oct 2026. About the data.

What to do

Advisories and patches

• lists.apache.org (Vendor advisory)

This summary is based on the CVE record as of 29 Oct 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

As listed in the CVE record.

Versions not listed are: unaffected.

Source: CVE List, as of 29 Oct 2026. About the data.

About this vulnerability

Inconsistent interpretation of HTTP requests (HTTP request/response smuggling) in the bundled HTTP/1.1 parser of Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to smuggle requests and inject headers when bRPC is deployed behind a proxy or load balancer that parses the same bytes differently. Root Cause: The bRPC fork of http-parser accepts and acts on several HTTP/1.1 he…

Summary: CVE record, as of 29 Oct 2026.

• CISA has not added CVE-2026-86146 to its Known Exploited Vulnerabilities (KEV) catalog, as of 29 Oct 2026.
• The CVE record was published on 21 Oct 2026.
• FIRST's EPSS model puts the probability of exploitation in the next 30 days at 0.2% (percentile 10.3), as of 29 Oct 2026. EPSS is a statistical estimate, not a report of exploitation.
• The credits in the CVE record name Anthropic (Claude) as finder.

Source: CISA KEV 2026.10.29, as of 29 Oct 2026; CVE List, as of 29 Oct 2026; FIRST EPSS, as of 29 Oct 2026. About the data.

Description

Apache bRPC: HTTP Request Smuggling and Header Injection via Lenient HTTP/1.1 Header Parsing

Inconsistent interpretation of HTTP requests (HTTP request/response smuggling) in the bundled HTTP/1.1 parser of Apache bRPC (version < 1.18.0) on all platforms allows remote attackers to smuggle requests and inject headers when bRPC is deployed behind a proxy or load balancer that parses the same bytes differently. Root Cause: The bRPC fork of http-parser accepts and acts on several HTTP/1.1 header forms that a conforming front-end either rejects or interprets differently, so the framing or the header set of a message can differ between the front-end and bRPC: 1. A space before the colon of framing headers (e.g. Content-Length : 5) is accepted; the value still drives bRPC's framing while the reported field name contains the trailing space. 2. Interior spaces inside a Content-Length value (e.g. Content-Length: 1 3) are skipped, so bRPC reads 13 where a front-end reads 1 or rejects the message (same class as CVE-2022-32213 in Node.js). 3. Obsolete line folding (obs-fold, RFC 7230 3.2.4) of Content-Length and Transfer-Encoding values is accepted, so a folded framing value drives bRPC's framing while a front-end that does not unfold sees a different message. 4. Chunked trailer fields are fed to the same header callbacks as the header section and are merged into the header map like real headers. A front-end only inspects the header section, so any chunked request can smuggle fields such as Authorization or X-Forwarded-For past it. 5. Transfer-Encoding lists with optional whitespace after a comma (e.g. Transfer-Encoding: gzip, chunked) are not recognized as chunked: such requests are rejected, and responses are read until connection close instead of as chunked, causing response desync. Affected Scenarios: bRPC server or client communicating over HTTP/1.1 with a front proxy, load balancer, or any peer that parses the message independently. An attacker able to send requests through the front-end can desynchronize the two parsers to smuggle requests, forge headers (e.g. Authorization, X-Forwarded-For) via chunked trailers, or desynchronize responses. How to Fix: (Choose one of the following options) 1. Upgrade bRPC to version 1.18.0, which fixes this issue. 2. Apply this patch: https://github.com/apache/brpc/pull/3521 Note: After applying the fix, the four header forms above are rejected by default and chunked trailers are dropped instead of merged into the header map. Two gflags are provided for compatibility: http_allow_obs_fold=true restores acceptance of folded Content-Length/Transfer-Encoding values, and http_strict_header_token=true additionally rejects spaces inside any header field name (not only the ones that decide framing). Legitimate clients that do not use these obsolete forms are unaffected.

Source: CVE List, as of 29 Oct 2026. About the data.

Timeline

Known exploited Apache vulnerabilities

• CVE-2016-3081: Apache Struts Command Injection Vulnerability (added 8 Oct 2026)
• CVE-2026-34486: Apache Tomcat Missing Encryption of Sensitive Data Vulnerability (added 4 Aug 2026)
• CVE-2026-34197: Apache ActiveMQ Improper Input Validation Vulnerability (added 16 Apr 2026)
• CVE-2024-38475: Apache HTTP Server Improper Escaping of Output Vulnerability (added 1 May 2025)
• CVE-2025-24813: Apache Tomcat Path Equivalence Vulnerability (added 1 Apr 2025)