fastapi-code-generator: Call-time RCE via operation summary -> unescaped route-handler docstring
Affects apps generated by fastapi-code-generator from specs that an attacker controls or influences, where an operation summary contains triple double quotes. Fixed in 0.8.1.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- Proof of concept public, per CISA
- Fix
- Fixed in 0.8.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 0.8.1.
- Exploitation15/40CISA rates a proof of concept as public
- Exposure20/25No login or user action needed, CISA rates it automatable · Data gap: Advisories don't say whether default setups are affected
- Reach?/20Reach: unknown (data gap). No tracked technology or package matched
- Severity10/10CVSS 9.3, total technical impact per CISA
- No patch0/5No signal
What would change the score
- Would score about 75 if added to CISA KEV
- Would score about 70 if CISA's SSVC rates exploitation active
- Would score about 50 if advisories confirm default setups are exposed
CVE-2026-63470 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.3 (critical) and affects fastapi-code-generator; fixed in 0.8.1.
- Last modified
- Where the record stands: published, rejected by its publisher, or superseded by another id.What do these mean? →
- Published
- Whether CISA lists it in its Known Exploited Vulnerabilities catalog: proof that attackers are using it.What do these mean? →
- Not listed in CISA KEV
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 45/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Unclear
- Fix
- Fixed in 0.8.1
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
- Exploitation: poc
- Automatable: yes
- Technical impact: total
Summary
fastapi-code-generator, a tool that builds FastAPI applications from OpenAPI specification files, is affected. An attacker who can influence an operation's summary field in an OpenAPI file can inject Python code that runs with the server's privileges when the affected route handler is called.
Read the original description
fastapi-code-generator creates FastAPI applications from OpenAPI files. Prior to 0.8.1, the generator inserts Operation.summary into a generated route-handler docstring as a triple-double-quoted string without escaping embedded triple quotes. An attacker-controlled or attacker-influenced operation summary can close the docstring and inject a valid Python expression statement into the handler body. Syntax-breaking input only causes generation to fail, but syntactically valid generated code executes with the server process's privileges when the affected route handler is called. This call-time route-handler docstring sink is distinct from the project's separate import-time route-path and additional-response-key sinks. This issue is fixed in version 0.8.1.
What to do
Upgrade to a fixed version: 0.8.1.
Timeline
- CVE published
- First seen by cve.now
- CISA SSVC assessment
Exploitation: poc · Automatable: yes · Technical impact: total
- Record last updated
- Posted on X by cve.now
Affected versions
- koxudaxi fastapi-code-generator
fixed in 0.8.1
Evidence 4
- Advisory
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-63470
Is CVE-2026-63470 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. CISA's SSVC assessment notes a proof of concept exists. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
An operation summary containing triple double quotes is written into the generated route handler's docstring without escaping. When the affected endpoint is invoked, this can run code on the server with the server process's privileges.Source: github.com
Which versions are affected by CVE-2026-63470?
fastapi-code-generator: before 0.8.1.Source: cve.now feed data
Am I affected, and how do I check?
Versions before 0.8.1 of fastapi-code-generator are in the affected range. The problem needs a generated app whose OpenAPI spec is attacker-controlled or attacker-influenced and has an operation summary with triple double quotes. To check a project, look at the fastapi-code-generator version used to generate it and the operation summaries in its spec.Source: github.com
How do I fix CVE-2026-63470?
Upgrade fastapi-code-generator to 0.8.1 or later.Source: github.com