CVE-2026-41178

EUVD-2026-34288 · Published May 28, 2026

opentelemetry-go's baggage parsing no longer caps raw header length

Summary

https://github.com/open-telemetry/opentelemetry-go/pull/7880 removed raw-length rejection and it causes Parse to process arbitrarily large/invalid baggage headers and log errors, enabling DoS via oversized inputs.

Details

The commit removes the upfront baggage-string length check and the per-member size guard in parsing. Parse now walks the entire input with strings.SplitSeq and skips invalid members while continuing to process the rest. For very large or malformed baggage headers, the parser still fully tokenizes and percent-decodes each member, and errors are forwarded to the global error handler (default logging). This lets a remote client send oversized/invalid headers to trigger excessive CPU/memory work and potentially large log output before any size limit is enforced, creating a denial-of-service risk in services that do not already enforce strict header size limits.

Summary:

In baggage/baggage.go, parseMember performs full parsing and PathUnescape on the entire member without any size guard, amplifying work for large inputs. Parse no longer checks bStr length and continues processing invalid members, so oversized/invalid headers are fully parsed instead of being rejected early.
In propagation/baggage.go, parsing errors from attacker-controlled headers are sent to the global error handler (default logging), which can amplify oversized-input impact.

PoC

baggage_dos_poc.tar.gz

Impact

The issue is reachable through standard propagation parsing (in-scope) and can be exploited remotely to cause CPU/log amplification, but the impact is availability-only and bounded by transport header limits and configurable error handling, supporting a medium severity rather than high/critical.

baggage.Parse iterates over all list members with strings.SplitSeq and skips invalid members while continuing, without a raw-length guard. parseMember performs full parsing and PathUnescape on each member, and propagation.Baggage forwards parsing errors to the global error handler, which logs by default. A remote client can therefore send oversized/invalid baggage headers that bypass the 8KB limit for valid members, causing extra CPU work and large log output, resulting in availability/log amplification in services that accept large headers and use the default handler.

Assumptions:

An instrumented service uses the OpenTelemetry baggage propagator for inbound request parsing.
Attackers can send oversized or malformed baggage headers that pass the hosting server/proxy header size limits.
The default error handler is used or logs are otherwise emitted for parse errors.
Inbound request parsing with propagation.Baggage
Oversized/invalid baggage headers accepted by the HTTP/gRPC stack
Error handler not suppressing parse errors

Technologies

Go.Opentelemetry.Io Otel PropagationGo.Opentelemetry.Io Otel BaggageOpentelemetry Opentelemetry

Weaknesses

CWE-789

CVSS scores

v3.15.3CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

MITRE ATT&CK

Inferred

Where this vulnerability fits in an attack

ReconImpact

Initial Access

T1190Exploit Public-Facing Application

References

Potentially impacted assets

See if this affects your attack surface

Latest trending attack

Criticalyesterday

Google Brotli decoder - Remote Code Execution via compressed requests (Exploitation Check)

This control is the second step of the Patrowl response to CVE-2026-111497 (Node2Shell). It complements the first control of 22 October 2026, which focused on the Node.js runtime, and does not replace it. Why a second control CVE-2026-111497 is an out-of-bounds write in the Google Brotli decoder, the library that decompresses Brotli ("br") data. It was first published as a Node.js vulnerability, because Node.js bundles this decoder. Later publications showed that the flaw is in the library itself. Every product that embeds an affected version of the decoder is concerned, whatever its language or vendor. A public proof of concept demonstrates code execution. Any server that decompresses request bodies sent with "Content-Encoding: br" exposes the decoder to unauthenticated attackers. Known cases include Express 5 and NestJS 11 on Node.js, Koa and Fastify setups, Bun, Envoy and Istio with request decompression enabled, and any application or reverse proxy that decodes Brotli request bodies with an affected library. The flaw also works in the other direction. A malicious server can compromise an unpatched client that decodes a Brotli response, for example Node.js fetch(), Python clients (requests, httpx, aiohttp, Scrapy) with the Brotli or brotlicffi package, or libcurl builds with Brotli support. What this control checks Patrowl sends small, valid Brotli-compressed requests to each asset and observes whether the server decodes them. The check does not depend on the technology: it detects the behaviour, whatever the stack behind it. These requests are what any legitimate client could send. They never reach the vulnerable code path and cannot affect the availability of the service. How to read the result Potentially impacted means the asset decodes Brotli request bodies: the attack surface is exposed. It does not confirm that the asset is vulnerable. The version of the Brotli decoder in use is not visible from the outside. This check covers applications that parse request bodies on their root path. A Not impacted result does not rule out exposure on other routes, nor on the client side. Checking the versions on the servers remains the only exhaustive verification. Affected and fixed versions Google Brotli 1.0.3 to 1.2.0 are affected, fixed in 1.0.10, 1.1.1 and 1.2.1. Fixed releases of the main products embedding it: Node.js 22.23.4, 24.22.1 and 26.12.1 (end-of-life lines 20.x and older and 25.x receive no fix), Bun 1.4.4, Envoy 1.37.8, 1.38.6, 1.39.3 and 1.40.0, Istio 1.29.9, 1.30.6 and 1.31.2, Python Brotli 1.2.1 and brotlicffi 1.2.1.0. Products that link against the system library depend on the Brotli package of the Linux distribution. Recommendations Update every component that embeds the Brotli decoder (only real fix). Start with the assets flagged by this control. Restart the processes after the update. Rebuild containers, single-executable applications and appliances that bundle an affected runtime or library. Reduce the exposure until the update is deployed. Reject requests with "Content-Encoding: br" at the reverse proxy, load balancer or WAF, case-insensitively and including lists such as "gzip, br". On Envoy and Istio, disable request decompression for Brotli. Review outbound calls. List the features that fetch content from servers you do not control, and patch the services that host them first.