What is CVE-2026-55407?

CVE-2026-55407 is a medium-severity uncontrolled resource consumption vulnerability in buffa (rust), affecting versions < 0.8.0. It is fixed in 0.8.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.

Which versions of buffa are affected by CVE-2026-55407?

buffa (rust) versions < 0.8.0 is affected.

Is there a fix for CVE-2026-55407?

Yes. CVE-2026-55407 is fixed in 0.8.0. Upgrade to this version or later.

Is CVE-2026-55407 exploitable, and should I be worried?

Whether CVE-2026-55407 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

What actually determines whether CVE-2026-55407 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

CVE-2026-55407 in buffa

Q: Which versions of buffa are affected by CVE-2026-55407?

buffa (rust) versions < 0.8.0 is affected.

Q: Is there a fix for CVE-2026-55407?

Yes. CVE-2026-55407 is fixed in 0.8.0. Upgrade to this version or later.

Q: Is CVE-2026-55407 exploitable, and should I be worried?

Whether CVE-2026-55407 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk.

Q: What actually determines whether CVE-2026-55407 is exploitable, and how bad it is?

Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.

Q: How do I fix CVE-2026-55407?

Upgrade buffa to 0.8.0 or later.

Summary

Buffa Vulnerable to Memory Exhaustion Denial of Service in decodeunknownfield via Unbounded Allocation

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.

Impact

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

Affected versions

buffa (< 0.8.0)

Security releases

buffa → 0.8.0 (rust)

Kodem intelligence

Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.

Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.

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Remediation advice

Upgrade buffa to 0.8.0 or later to resolve this vulnerability.

Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.

Frequently Asked Questions

What is CVE-2026-55407? CVE-2026-55407 is a medium-severity uncontrolled resource consumption vulnerability in buffa (rust), affecting versions < 0.8.0. It is fixed in 0.8.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
Which versions of buffa are affected by CVE-2026-55407? buffa (rust) versions < 0.8.0 is affected.
Is there a fix for CVE-2026-55407? Yes. CVE-2026-55407 is fixed in 0.8.0. Upgrade to this version or later.
Is CVE-2026-55407 exploitable, and should I be worried? Whether CVE-2026-55407 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
What actually determines whether CVE-2026-55407 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
How do I fix CVE-2026-55407? Upgrade buffa to 0.8.0 or later.