CVE-2026-54277
Description
A flaw was found in aiohttp, an asynchronous HTTP client/server framework for Python. A remote attacker can exploit this vulnerability by sending oversized lines within an HTTP request. This bypasses the max_line_size check in the C parser, causing the system to use an excessive amount of memory. This can lead to a Denial of Service (DoS) condition, making the affected system unavailable.
Statement
This vulnerability is rated Moderate because an unauthenticated remote attacker can trigger denial of service against an affected aiohttp HTTP server that uses the default C-based parser, by sending HTTP requests with oversized fragmented lines that bypass max_line_size limits, causing excessive memory consumption. Exploitation requires aiohttp to be deployed as a network-facing HTTP server using the optimised C parser (the default in pre-built wheels).
Many Red Hat products ship aiohttp as a bundled dependency for client libraries, internal automation, or services that do not expose this server/parser path to untrusted users. In those configurations, practical risk may be lower, but affected packages should still be updated to aiohttp 3.14.1 or later when fixes are released.
Mitigation
Update the aiohttp package to version 3.14.1 or later.
Until updated builds are available, reduce exposure by not exposing aiohttp-based HTTP servers directly to untrusted networks. As a workaround, configure aiohttp to use the pure-Python HTTP parser by setting use_cparser=False when creating the application or running the server. This avoids the vulnerable C parser path. Installations that use aiohttp only as an HTTP client are not affected by this flaw.
Common Vulnerability Scoring System (CVSS) Score Details
Info alert:Important note
CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).
The following CVSS metrics and score provided are preliminary and subject to review.
CVSS v3 Score Breakdown
| Red Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.9 | 7.5 | N/A |
| Attack Vector | Network | Network | N/A |
| Attack Complexity | High | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | None | None | N/A |
| Scope | Unchanged | Unchanged | N/A |
| Confidentiality | None | None | N/A |
| Integrity Impact | None | None | N/A |
| Availability Impact | High | High | N/A |
Vector
Red Hat: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
NVD: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Understanding the Weakness (CWE)
Integrity,Availability,Confidentiality
Technical Impact: DoS: Crash, Exit, or Restart; Execute Unauthorized Code or Commands; Read Memory; Modify Memory
If the incorrect calculation is used in the context of memory allocation, then the software may create a buffer that is smaller or larger than expected. If the allocated buffer is smaller than expected, this could lead to an out-of-bounds read or write (CWE-119), possibly causing a crash, allowing arbitrary code execution, or exposing sensitive data.
Frequently Asked Questions
Not sure what something means? Check out our Security Glossary.
Want to get errata notifications? Sign up here.
