GHSA-mh2q-q3fh-2475 CVE-2026-29181 GO-2026-5506

OpenTelemetry-Go: multi-value `baggage` header extraction causes excessive allocations (remote dos amplification)

High Go

Severity: 7.5 / 10; High · CVSS 3.1
Exploit chance (EPSS): 0.79%; Chance of exploitation in the next 30 days. Higher than 56.28% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-400 Uncontrolled Resource Consumption; CWE-770 Allocation of Resources Without Limits or Throttling
Fix: 1.41.0; Upgrade go.opentelemetry.io/otel to this version or later

Description

multi-value baggage: header extraction parses each header field-value independently and aggregates members across values. this allows an attacker to amplify cpu and allocations by sending many baggage: header lines, even when each individual value is within the 8192-byte per-value parse limit.

severity

HIGH (availability / remote request amplification)

relevant links

repository: https://github.com/open-telemetry/opentelemetry-go
pinned callsite: https://github.com/open-telemetry/opentelemetry-go/blob/1ee4a4126dbdd1bc79e9fae072fa488beffac52a/propagation/baggage.go#L58

vulnerability details

pins: open-telemetry/opentelemetry-go@1ee4a4126dbdd1bc79e9fae072fa488beffac52a as-of: 2026-02-04 policy: direct (no program scope provided)

callsite: propagation/baggage.go:58 (extractMultiBaggage) attacker control: inbound HTTP request headers (many baggage field-values) → propagation.HeaderCarrier.Values("baggage") → repeated baggage.Parse + member aggregation

root cause

extractMultiBaggage iterates over all baggage header field-values and parses each one independently, then appends members into a shared slice. the 8192-byte parsing cap applies per header value, but the multi-value path repeats that work once per header line (bounded only by the server/proxy header byte limit).

impact

in a default net/http configuration (max header bytes 1mb), a single request with many baggage: header field-values can cause large per-request allocations and increased latency.

example from the attached PoC harness (darwin/arm64; 80 values; 40 requests):

canonical: per_req_alloc_bytes=10315458 and p95_ms=7
control: per_req_alloc_bytes=133429 and p95_ms=0

proof of concept

canonical:

mkdir -p poc
unzip poc.zip -d poc
cd poc
make test

output (excerpt):

[CALLSITE_HIT]: propagation/baggage.go:58 extractMultiBaggage
[PROOF_MARKER]: baggage_multi_value_amplification p95_ms=7 per_req_alloc_bytes=10315458 per_req_allocs=16165

control:

cd poc
make control

control output (excerpt):

[NC_MARKER]: baggage_single_value_baseline p95_ms=0 per_req_alloc_bytes=133429 per_req_allocs=480

expected: multiple baggage header field-values should be semantically equivalent to a single comma-joined baggage value and should not multiply parsing/alloc work within the effective header byte budget. actual: multiple baggage header field-values trigger repeated parsing and member aggregation, causing high per-request allocations and increased latency even when each individual value is within 8192 bytes.

fix recommendation

avoid repeated parsing across multi-values by enforcing a global budget and/or normalizing multi-values into a single value before parsing. one mitigation approach is to treat multi-values as a single comma-joined string and cap total parsed bytes (for example 8192 bytes total).

fix accepted when: under the default PoC harness settings, canonical stays within 2x of control for per_req_alloc_bytes and per_req_allocs, and p95_ms stays below 2ms.

poc.zip PR_DESCRIPTION.md

Affected versions

Go

Package	Vulnerable	Fixed in
go.opentelemetry.io/otel	`>= 1.36.0, <= 1.40.0`	No fix yet
go.opentelemetry.io/otel	`>= 1.36.0, < 1.41.0`	`1.41.0`

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

go.opentelemetry.io/otel Go → `1.41.0`

go

go get go.opentelemetry.io/otel@v1.41.0 && go mod tidy

Severity breakdown

CVSS 3.1 7.5

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Weakness

CWE-400: Uncontrolled Resource Consumption

The product does not properly control the allocation and maintenance of a limited resource.

How to prevent it

Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, or uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution is simply difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply makes the attack require more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Implementation: Ensure that all failures in resource allocation place the system into a safe posture.

CWE-770: Allocation of Resources Without Limits or Throttling

The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

How to prevent it

Requirements: Clearly specify the minimum and maximum expectations for capabilities, and dictate which behaviors are acceptable when resource allocation reaches limits.
Architecture and Design: Limit the amount of resources that are accessible to unprivileged users. Set per-user limits for resources. Allow the system administrator to define these limits. Be careful to avoid CWE-410.
Architecture and Design: Design throttling mechanisms into the system architecture. The best protection is to limit the amount of resources that an unauthorized user can cause to be expended. A strong authentication and access control model will help prevent such attacks from occurring in the first place, and it will help the administrator to identify who is committing the abuse. The login application should be protected against DoS attacks as much as possible. Limiting the database access, perhaps by caching result sets, can help minimize the resources expended. To further limit the potential for a DoS attack, consider tracking the rate of requests received from users and blocking requests that exceed a defined rate threshold.
Implementation: Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does. When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue." Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
Architecture and Design: For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Architecture and Design: Mitigation of resource exhaustion attacks requires that the target system either: recognizes the attack and denies that user further access for a given amount of time, typically by using increasing time delays uniformly throttles all requests in order to make it more difficult to consume resources more quickly than they can again be freed. The first of these solutions is an issue in itself though, since it may allow attackers to prevent the use of the system by a particular valid user. If the attacker impersonates the valid user, they may be able to prevent the user from accessing the server in question. The second solution can be difficult to effectively institute -- and even when properly done, it does not provide a full solution. It simply requires more resources on the part of the attacker.
Architecture and Design: Ensure that protocols have specific limits of scale placed on them.
Architecture and Design, Implementation: If the program must fail, ensure that it fails gracefully (fails closed). There may be a temptation to simply let the program fail poorly in cases such as low memory conditions, but an attacker may be able to assert control before the software has fully exited. Alternately, an uncontrolled failure could cause cascading problems with other downstream components; for example, the program could send a signal to a downstream process so the process immediately knows that a problem has occurred and has a better chance of recovery. Ensure that all failures in resource allocation place the system into a safe posture.
Operation, Architecture and Design: Use quotas or other resource-limiting settings provided by the operating system or environment. For example, when managing system resources in POSIX, setrlimit() can be used to set limits for certain types of resources, and getrlimit() can determine how many resources are available. However, these functions are not available on all operating systems. When the current levels get close to the maximum that is defined for the application (see CWE-770), then limit the allocation of further resources to privileged users; alternately, begin releasing resources for less-privileged users. While this mitigation may protect the system from attack, it will not necessarily stop attackers from adversely impacting other users. Ensure that the application performs the appropriate error checks and error handling in case resources become unavailable (CWE-703).

References

Advisories

Fixes and patches

Packages

github.com/open-telemetry/opentelemetry-go

Timeline

Apr 7, 2026 Published
Sep 11, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GO-2026-5158 opentelemetry-go's baggage parsing no longer caps raw header length	Medium	Also affects go.opentelemetry.io/otel
GHSA-cggf-277g-3q54 pypdf has possible large memory usage when parsing page tree	High	Same weakness, CWE-400
GHSA-3g3m-2fjr-6pw4 Glob: AbortSignal cancellation bypass allows post-timeout filesystem traversal	Medium	Same weakness, CWE-400
GHSA-42gh-23hr-vphw pypdf has possible long runtimes when retrieving page labels	High	Same weakness, CWE-400
GHSA-4vqv-7265-gm2w pypdf has possible large memory usage for exceptions in strict mode	High	Same weakness, CWE-400
GHSA-62m5-6wh8-28x7 pypdf has possible long runtimes/large memory usage for encrypted PDF files	High	Same weakness, CWE-400
GHSA-7wch-p9px-956x Forge: Regular expression denial of service in PEM decoding (pem.decode)	High	Same weakness, CWE-400
GHSA-fw5c-8223-6h42 russh: peer-declared zero maximum packet size permanently stalls channel writes (silent AsyncWrite hang)	Medium	Same weakness, CWE-400

Credits: 1seal, Ankush-Pathak, XSAM

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