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GHSA-28jh-g32x-v9v4 CVE-2026-48598 EEF-CVE-2026-48598

Tesla vulnerable to multipart part smuggling via unescaped `content-disposition` values

Low Hex
Severity
0.0 / 10
Low · CVSS 4.0
Exploit chance (EPSS)
0.27%
Chance of exploitation in the next 30 days. Higher than 19.74% of scored vulnerabilities.
Known exploited
No
Not in CISA's catalog
Weakness
CWE-116 Improper Encoding or Escaping of Output
Fix
1.18.3
Upgrade tesla to this version or later

Description

Summary

Tesla.Multipart.part_headers_for_disposition/1 interpolates Content-Disposition parameter values (field name, filename, and other opts) verbatim into the part header line without encoding or escaping any special characters. An attacker who controls a filename, field name, or other disposition parameter can use unescaped double-quotes to inject extra disposition key-value pairs, or CRLF sequences to inject additional part headers or prepend bytes to the part body.

Details

part_headers_for_disposition/1 in lib/tesla/multipart.ex formats each disposition parameter as k="v" with no sanitization. Values flow in from add_field/4 (the name argument), add_file/3 and add_file_content/4 (the filename argument and any disposition opts). A " in the value closes the quoted parameter early, allowing extra ; key="value" pairs to be appended. A \r\n ends the Content-Disposition header line entirely, with subsequent bytes interpreted as additional part headers (e.g. a forged Content-Type); a second \r\n ends the whole part header block and prepends attacker bytes to the part body.

The default-filename path in add_file/3 derives the name via Path.basename/1, which does not strip CR or LF, so any code that forwards a partially attacker-controlled file path is equally vulnerable.

PoC

  1. Call Tesla.Multipart.add_file_content/4 with a filename containing \r\nX-Injected: evil.
  2. POST the multipart body to any upstream via any Tesla adapter.
  3. The upstream receives X-Injected: evil as a standalone header line on the affected part.

Impact

Low severity (CVSS v4.0: 2.1). Any application using tesla 0.8.0 through 1.18.2 that passes untrusted input into add_field/4, add_file/3, or add_file_content/4 disposition parameters is affected. Consequences range from forging part-level headers to body prepending against lenient multipart parsers. Fixed in tesla 1.18.3.

Workarounds

Validate disposition parameter values before passing them to the multipart API, rejecting any value that contains \r, \n, or ".

Resources

Affected versions

Hex

PackageVulnerableFixed in
tesla
>= 0.8.0, < 1.18.3
1.18.3

How to fix

Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.

tesla Hex → 1.18.3

mix
{:tesla, "~> 1.18.3"} # then: mix deps.update tesla

Severity breakdown

CVSS 4.0 0.0

CVSS:4.0/AV:L/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:N/SC:N/SI:L/SA:N

Attack vector
Local
Attack complexity
Low
Attack requirements
Present
Privileges required
None
User interaction
None
Confidentiality (vulnerable system)
None
Integrity (vulnerable system)
None
Availability (vulnerable system)
None
Confidentiality (subsequent systems)
None
Integrity (subsequent systems)
Low
Availability (subsequent systems)
None

CVSS 3.1 3.7

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

Attack vector
Network
Attack complexity
High
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
Low
Availability
None

Weakness

CWE-116: Improper Encoding or Escaping of Output

The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

How to prevent it
  • Architecture and Design: Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error. Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
  • Architecture and Design: If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated. For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
  • Architecture and Design, Implementation: Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
  • Architecture and Design: In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.
  • Architecture and Design: Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
  • Requirements: Fully specify which encodings are required by components that will be communicating with each other.
  • Implementation: When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.

References

Advisories

Fixes and patches

Packages

Other links

Timeline

  1. Published
  2. Last updated by the source
  3. Latest EPSS score
AdvisorySeverityWhy it's related
EEF-CVE-2026-48596
CRLF injection in Tesla.Multipart.add_content_type_param/2 allows HTTP header injection
Low Also affects tesla
EEF-CVE-2026-48594
Decompression bomb in Tesla.Middleware.DecompressResponse and Tesla.Middleware.Compression
High Also affects tesla
EEF-CVE-2026-48595
Authorization header leaks to third-party origin on cross-origin redirect in Tesla.Middleware.FollowRedirects
Medium Also affects tesla
EEF-CVE-2026-48597
Atom table exhaustion via untrusted URL scheme in Tesla.Adapter.Mint
Medium Also affects tesla
GHSA-qxg6-89mg-rqv8
Vitest: Code injection via unauthenticated manual mock registration
Medium Same weakness, CWE-116
GHSA-333x-w4r6-6crp
fast-uri vulnerable to scheme injection via an unescaped first-segment colon in suffix references
Low Same weakness, CWE-116
GHSA-xw65-4hp5-5hc7
Handlebars: JavaScript Injection via Unsafe Inline Embedding of Precompiled Templates
Medium Same weakness, CWE-116
GHSA-wx4j-mvgx-mqwp
Satori-generated SVG has improper escaping
Medium Same weakness, CWE-116

Credits: Jonatan Männchen / EEF, Peter Ullrich, Yordis Prieto

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