EEF-CVE-2026-42788 CVE-2026-42788 GHSA-q6v9-r226-v65f

HTTP/2 frame size limit checked after body is buffered in bandit

Medium Hex

Severity: 0.0 / 10; Medium · CVSS 4.0
Exploit chance (EPSS): 0.51%; Chance of exploitation in the next 30 days. Higher than 43.50% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-770 Allocation of Resources Without Limits or Throttling
Fix: 1.11.0; Upgrade bandit to this version or later

Description

Summary

Allocation of Resources Without Limits or Throttling vulnerability in mtrudel bandit allows unauthenticated memory exhaustion via oversized HTTP/2 frames.

'Elixir.Bandit.HTTP2.Frame':deserialize/2 in lib/bandit/http2/frame.ex checks the SETTINGS_MAX_FRAME_SIZE limit only after pattern-matching payload::binary-size(length), which requires the entire frame body to be present in memory before either the accept or reject clause can fire. A peer that announces a frame length up to the 24-bit maximum (~16 MiB) causes the server to buffer that entire body before the size guard is evaluated, regardless of the max_frame_size negotiated during the HTTP/2 handshake (default 16 KiB per RFC 9113).

An unauthenticated attacker holding many concurrent connections can force the server to buffer far more memory than the negotiated frame size limit should permit, leading to memory pressure and potential denial of service.

This issue affects bandit: from 0.3.6 before 1.11.0.

Affected versions

Hex

Package	Vulnerable	Fixed in
bandit	`>= 0.3.6, < 1.11.0`	`1.11.0`
bandit	`>= 0.3.5, < 1.11.0`	`1.11.0`

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.

bandit Hex → `1.11.0`

mix

{:bandit, "~> 1.11.0"} # then: mix deps.update bandit

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Attack vector: Network
Attack complexity: Low
Attack requirements: None
Privileges required: None
User interaction: None
Confidentiality (vulnerable system): None
Integrity (vulnerable system): None
Availability (vulnerable system): Low
Confidentiality (subsequent systems): None
Integrity (subsequent systems): None
Availability (subsequent systems): None

Weakness

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

github.com/mtrudel/bandit/commit/1e8e55966da9129016b73d32f0e1df4630e3b463

Packages

Timeline

May 1, 2026 Published
Oct 26, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
EEF-CVE-2026-116078 HTTP/2 request bodies made of 1-byte DATA frames amplify memory use in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-108529 SETTINGS and stream-0 WINDOW_UPDATE frames trigger quadratic work over blocked streams in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-110499 Client-chosen HPACK encoder table size is applied uncapped, growing per-connection state with every response in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-109584 HTTP/2 cookie crumb join expands a small HPACK header block into an unbounded allocation in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-111103 HTTP/2 StreamError recovery rolls back connection state and bypasses per-connection limits in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-111101 HTTP/1.1 chunked request bodies made of 1-byte chunks amplify memory use in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-113436 Quadratic bignum parsing of Content-Length and Host port values in Bandit	Not rated yet	Also affects bandit
EEF-CVE-2026-110314 WebSocket frames keep reaching the WebSock after a server-initiated close in Bandit	Not rated yet	Also affects bandit

Credits: Jonatan Männchen / EEF, Mat Trudel, Peter Ullrich

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