Summary
HTTPX2: Multipart part header injection via unvalidated file Content-Type and custom headers
HTTPX2 serializes the per-file Content-Type and custom headers supplied through the files= tuple API directly into the multipart/form-data body without validating custom header names or values. An attacker who can influence upload metadata passed to HTTPX2 can use CR or LF characters to terminate a multipart part header and inject additional part headers or end the part header block early.
Details
The three-element file tuple accepts (filename, content, content_type), and the four-element form accepts (filename, content, content_type, headers). FileField.render_headers() interpolates the supplied header names and values between CRLF delimiters without validating them.
For example:
import httpx2
request = httpx2.Request(
"POST",
"https://example.com/upload",
headers={"Content-Type": "multipart/form-data; boundary=BOUNDARY"},
files={
"file": (
"safe.txt",
b"payload",
"text/plain\r\nX-Injected: true",
)
},
)
print(request.read().decode())
The generated body contains an attacker-injected part header:
--BOUNDARY
Content-Disposition: form-data; name="file"; filename="safe.txt"
Content-Type: text/plain
X-Injected: true
payload
--BOUNDARY--
The same issue affects names and values in the custom header mapping from the four-element tuple.
Field names and filenames are serialized through a separate escaping path and do not permit CRLF header injection.
Mitigation
Upgrade to HTTPX2 2.11.0 or later. Patched versions reject forbidden control characters in multipart part header names and values and raise ValueError before serializing the request.
If upgrading is not immediately possible, applications should validate custom multipart header names as HTTP field-name tokens. They should reject NUL, CR, LF, other C0 controls except horizontal tab, and DEL in per-file content types and custom header values before passing them to HTTPX2.
Impact
Applications are affected when they pass attacker-controlled upload metadata into the per-file content_type or custom headers arguments. The receiving server interprets injected lines as genuine multipart part headers. Depending on how that server validates and processes uploads, this can alter part semantics or bypass checks based on part headers.
This does not split the outer HTTP request: the injected headers are contained within the multipart body. The concrete security impact therefore depends on the downstream multipart parser and application behavior.
CVE-2026-84379 has a CVSS score of 5.3 (Medium). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.11.0); upgrading removes the vulnerable code path.
Affected versions
Security releases
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.
Already deployed Kodem?
See it in your environmentNew to Kodem? Get a demo →Remediation advice
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-84379? CVE-2026-84379 is a medium-severity security vulnerability in httpx2 (pip), affecting versions < 2.11.0. It is fixed in 2.11.0.
- How severe is CVE-2026-84379? CVE-2026-84379 has a CVSS score of 5.3 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of httpx2 are affected by CVE-2026-84379? httpx2 (pip) versions < 2.11.0 is affected.
- Is there a fix for CVE-2026-84379? Yes. CVE-2026-84379 is fixed in 2.11.0. Upgrade to this version or later.
- Is CVE-2026-84379 exploitable, and should I be worried? Whether CVE-2026-84379 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-2026-84379 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-2026-84379? Upgrade
httpx2to 2.11.0 or later.