CVE-2026-55407: Buffa Denial of Service Vulnerability

MODERATE
Advisory Identifier: GHSA-f9qc-qg88-7pq5
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CWE-789 CWE-400 CWE-770
Published
Advisory Summary

CVE-2026-55407 is a MODERATE denial of service vulnerability (CWE-789: Memory Allocation with Excessive Size Value) affecting Buffa libraries in the crates.io ecosystem. The issue involves buffa vulnerable to memory exhaustion denial of service in decode_unknown_field via unbounded allocation. Remediation is available by upgrading affected packages to version 0.8.0.

CVE-2026-55407 at a Glance

CVE Identifier CVE-2026-55407
GHSA Identifier GHSA-f9qc-qg88-7pq5
Severity MODERATE
CVSS v3.1 Base Score N/A
CWE Classification CWE-789: Memory Allocation with Excessive Size Value
Affected Product Buffa
Package Ecosystem crates.io
Published Date
Last Updated

How to Fix CVE-2026-55407

To remediate this vulnerability, upgrade all affected Buffa dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

buffa fixed: 0.8.0 
Upgrade buffa to 0.8.0
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for buffa

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-55407, inspect your project dependencies for Buffa:

inspect dependencies for buffa

Analyze the terminal output to locate any version of Buffa in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 0.8.0), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-789: Memory Allocation with Excessive Size Value, where the product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated. In Buffa, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

The `decode_unknown_field` function in buffa's protobuf decoder allocated heap memory in proportion to untrusted input (unknown fields in the serialized protobuf) without enforcing an allocation budget. Any message decoded from untrusted input using code generated with `preserve_unknown_fields=true` (the default) was affected. A small, well-formed payload of nested unknown fields inside a StartGroup could trigger roughly 22× memory amplification (e.g., a 64 MiB input forcing ~1.4 GB of heap allocation), and length-delimited unknown fields could be sized arbitrarily, enabling an unauthenticated attacker to crash a process via memory exhaustion. This was reachable from the default decode APIs, since the top-level message size cap did not account for in-decode amplification. For users of connectrpc - the DEFAULT_MAX_MESSAGE_SIZE for connectrpc is 4MiB, which limits amplification in the worst case to ~88 MiB of memory. A flood of concurrent requests with this pattern could still be used to exhaust available memory, however. Users are advised to either set `preserve_unknown_fields=false` on their current generated code, or upgrade to 0.8.0, which enforces per-message unknown field count limits - this is configurable, with a default of 1 million unknown fields, or ~40MiB of allocation overhead per message. Users are advised to update to the latest version, which enforces per-message unknown field count limits. Thank you to @p80n-sec for reporting this issue.

CVE-2026-55407 Affected Buffa Versions

1 component(s)
Fixed Versions:
0.8.0
Product / Package Ecosystem Affected Versions Fixed Version
buffa
 crates.io
< 0.8.0
0.8.0

References

GitHub Advisory / Wiki ADVISORY
https://github.com/anthropics/buffa/security/advisories/GHSA-f9qc-qg88-7pq5
NVD — CVE-2026-55407 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-55407
Buffa Source Repository REPOSITORY
https://github.com/anthropics/buffa/pull/184
Security Fix Commit FIX COMMIT
https://github.com/anthropics/buffa/commit/278fa43fcff661d4ee6bd83b75955a153d4281fc
Buffa Source Repository REPOSITORY
https://github.com/anthropics/buffa
Buffa Release RELEASE
https://github.com/anthropics/buffa/releases/tag/v0.8.0

Frequently Asked Questions

What is CVE-2026-55407?
CVE-2026-55407 is a security vulnerability in Buffa involving Buffa Vulnerable to Memory Exhaustion Denial of Service in decode_unknown_field via Unbounded Allocation under CWE-789: Memory Allocation with Excessive Size Value.
Which Buffa versions are affected?
Affected versions include releases prior to 0.8.0 across affected packages: buffa.
What version fixes CVE-2026-55407?
Upgrading to 0.8.0 (or the latest patched release for your respective branch) resolves the vulnerability.
Is buffa affected?
Yes, buffa is affected in releases prior to 0.8.0. Upgrade your dependency to 0.8.0 or later.
What CWE is associated with CVE-2026-55407?
CVE-2026-55407 is classified under CWE-789: Memory Allocation with Excessive Size Value (The product allocates memory based on an untrusted, large size value, but it does not ensure that the size is within expected limits, allowing arbitrary amounts of memory to be allocated.).
How can I check crates.io dependencies for CVE-2026-55407?
Run the dependency tree command: 'inspect dependencies for buffa'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-f9qc-qg88-7pq5",
  "modified" : "2026-08-28T18:34:22Z",
  "published" : "2026-08-28T18:34:22Z",
  "aliases" : [ "CVE-2026-55407" ],
  "summary" : "Buffa Vulnerable to Memory Exhaustion Denial of Service in decode_unknown_field via Unbounded Allocation",
  "details" : "The `decode_unknown_field` function in buffa's protobuf decoder allocated heap memory in proportion to untrusted input (unknown fields in the serialized protobuf) without enforcing an allocation budget. Any message decoded from untrusted input using code generated with `preserve_unknown_fields=true` (the default) was affected. A small, well-formed payload of nested unknown fields inside a StartGroup could trigger roughly 22× memory amplification (e.g., a 64 MiB input forcing ~1.4 GB of heap allocation), and length-delimited unknown fields could be sized arbitrarily, enabling an unauthenticated attacker to crash a process via memory exhaustion. This was reachable from the default decode APIs, since the top-level message size cap did not account for in-decode amplification. \n\nFor users of connectrpc - the DEFAULT_MAX_MESSAGE_SIZE for connectrpc is 4MiB, which limits amplification in the worst case to ~88 MiB of memory. A flood of concurrent requests with this pattern could still be used to exhaust available memory, however.\n\nUsers are advised to either set `preserve_unknown_fields=false` on their current generated code, or upgrade to 0.8.0, which enforces per-message unknown field count limits - this is configurable, with a default of 1 million unknown fields, or ~40MiB of allocation overhead per message.\nUsers are advised to update to the latest version, which enforces per-message unknown field count limits.\n\nThank you to @p80n-sec for reporting this issue.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "crates.io",
      "name" : "buffa"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "0.8.0"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/anthropics/buffa/security/advisories/GHSA-f9qc-qg88-7pq5"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-55407"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/anthropics/buffa/pull/184"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/anthropics/buffa/commit/278fa43fcff661d4ee6bd83b75955a153d4281fc"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/anthropics/buffa"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/anthropics/buffa/releases/tag/v0.8.0"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-400", "CWE-770", "CWE-789" ],
    "severity" : "MODERATE",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-08-28T18:34:22Z",
    "nvd_published_at" : "2026-07-16T17:16:57Z"
  }
}