Http4s: ResourceService and Webjar Service path escape via percent-encoded separators
Http4s is a Scala interface for HTTP services. Prior to 0.23.35 and 1.0.0-M47, ResourceService and WebjarService decode each URL path segment but reject only segments exactly equal to an empty string, a dot, or two dots. A request containing percent-encoded slash or backslash separators can turn an accepted segment into a parent-directory traversal after decoding, allowing access to classpath or WebJar resources outside the configured base when a directory-backed classpath is served and the backend preserves the encoded separator. The patch rejects decoded segments containing slash or backslash in ResourceService and WebjarService, and applies the same guard to the non-exploitable FileService for consistency. This issue is fixed in versions 0.23.35 and 1.0.0-M47.
- Published
- Sep 15, 2026
- Updated
- Sep 16, 2026
- EPSS
- 0.8% · 54th percentile
- CWE
- CWE-22
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Report tools
Action score
23
Monitor
Low priority for now.
- CVSS
- 23 / 40 · 5.9 / 10
- CISA KEV
- 0 / 30 · Not listed
- EPSS
- 0 / 30 · 0.8%
CISA SSVC decision
- Exploitation
- none
- Automatable
- no
- Technical impact
- partial
Vulnrichment: CISA's decision-tree inputs.
CNA vs NVD score
- NVD
- —
- CNA · GitHub_M
- 5.9
- NVD has not scored this yet; the score shown is the CNA’s.
The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.
Noroxi analysis
No Noroxi analysis for this record yet
We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.
We use this product, ask for helpAffected systems
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Versions reported by the vendor
Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.
http4s http4s
- < 0.23.35, >= 1.0.0-M1, < 1.0.0-M47affected
Package-level exposure
OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.
| Ecosystem | Package | Affected range | Fix |
|---|---|---|---|
| Maven | org.http4s:http4s-server_2.12 | before 0.23.35 | 0.23.35 |
| Maven | org.http4s:http4s-server_2.13 | from 1.0.0-M1 · before 1.0.0-M47 | 1.0.0-M47 |
| Maven | org.http4s:http4s-server_2.13 | before 0.23.35 | 0.23.35 |
| Maven | org.http4s:http4s-server_3 | from 1.0.0-M1 · before 1.0.0-M47 | 1.0.0-M47 |
| Maven | org.http4s:http4s-server_3 | before 0.23.35 | 0.23.35 |
Same product
http4s: all recordsOther highest-scoring records for the same primary product.
- CVE-2026-69204Http4s: Ember accepts Transfer-Encoding combined with Content-Length (CL.TE request smuggling)36Monitor
- CVE-2026-69217Http4s: Ember Server accepts duplicate Content-Length headers34Monitor
- CVE-2026-69205Http4s: Ember Transfer-Encoding value parsing (TE.CL / TE.0 request smuggling)34Monitor
- CVE-2026-54556Http4s: HTTP/2 Denial of Service with Ember Backend32Monitor
- CVE-2026-88975Http4s: Ember HTTP/2 buffers a frame's declared payload before checking SETTINGS_MAX_FRAME_SIZE30Monitor
- CVE-2026-69218Http4s Ember HTTP/2: unbounded continuation frame accumulation30Monitor
Remediation
Which version to upgrade to
Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.
| Product / package | Fixed version | Source |
|---|---|---|
| Maven:org.http4s:http4s-server_2.12 | 0.23.35 | Package registry (OSV) |
| Maven:org.http4s:http4s-server_2.13 | 0.23.35 | Package registry (OSV) |
| Maven:org.http4s:http4s-server_2.13 | 1.0.0-M47 | Package registry (OSV) |
| Maven:org.http4s:http4s-server_3 | 0.23.35 | Package registry (OSV) |
| Maven:org.http4s:http4s-server_3 | 1.0.0-M47 | Package registry (OSV) |
Exploit status
No known public exploit
No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.
Research context
For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.
Timeline
From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.
No dated events beyond publication.
FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).
Patch and commit links
Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.
Credits
All researchersFinders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.
No credits in the CNA record.
Variant candidates
Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.
No nightly-computed relations.
Chain candidates
An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.
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Bug bounty scope
No known public program.
Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).
Technical details
Attack conditions
- Anyone who can reach it over the internet can trigger it.
- No account or password is required.
- No user action is required.
- Special conditions such as timing or configuration are required.
If successful
- Confidentiality
- high · data can be read
- Integrity
- none
- Availability
- none
- Attack vector
- Network
- Attack complexity
- High
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality impact
- High
- Integrity impact
- None
- Availability impact
- None
Weakness class (CWE)
CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
nvd-secondary
Root cause
A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.
The bug in code
The whole CWE-22 classA representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.
Vulnerable
const file = path.join(ROOT, req.query.name);res.sendFile(file);Fixed
const file = path.resolve(ROOT, req.query.name);if (!file.startsWith(ROOT + path.sep)) { return res.sendStatus(400);}res.sendFile(file);Attack context
MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.
Attack patterns (CAPEC)
- Path TraversalCAPEC-126likelihood: High · Very High
- Using Slashes and URL Encoding Combined to Bypass Validation LogicCAPEC-64likelihood: High · High
- Manipulating Web Input to File System CallsCAPEC-76likelihood: High · Very High
- Using Escaped Slashes in Alternate EncodingCAPEC-78likelihood: High · High
- Using Slashes in Alternate EncodingCAPEC-79likelihood: High · High
ATT&CK techniques
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Change log
- Fix✗ → ✓
For records you follow, these changes also arrive as notifications. →
References
- github.com/http4s/http4s/commit/bcd99cdc1342ef58a0f132acb814af06a668a8d3
- github.com/http4s/http4s/releases/tag/v0.23.35
- github.com/http4s/http4s/releases/tag/v1.0.0-M47
- github.com/http4s/http4s/security/advisories/GHSA-crq5-92j2-j7wv
Vendor advisories and official records. Exploit/PoC links are deliberately left out.