Answer in brief
CVE-2026-73495 records a High severity (CVSS 7.4) vulnerability in blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass). The current sources do not mark it as known exploited. The current feed maps http4s/blaze (generic), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.13 (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
Answer in brief
CVE-2026-73495 records a High severity (CVSS 7.4) vulnerability in blaze: Chunked-body trailer fields promoted into Request.headers in blaze-server (front-end header-sanitization bypass). The current sources do not mark it as known exploited. The current feed maps http4s/blaze (generic), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.13 (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps http4s/blaze (generic), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.13 (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| http4s/blazegeneric | < 0.23.18 || >= 1.0.0-M1, < 1.0.0-M42 | Not reported |
| org.http4s:blaze-http_2.12maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_2.12maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=1.0.0-M1 <1.0.0-M42 | 1.0.0-M42 |
| org.http4s:blaze-http_2.13maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=1.0.0-M1,<=1.0.0-M41 | 1.0.0-M42 |
| org.http4s:blaze-http_3maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_3maven | >=1.0.0-M1 <1.0.0-M42 | 1.0.0-M42 |
| org.http4s:blaze-http_3maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_3maven | >=1.0.0-M1,<1.0.0-M42 | 1.0.0-M42 |
Published upstream
Aug 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 8, 2026
blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and 1.0.0-M42, blaze-server can merge HTTP/1.1 chunked-body trailer fields into Request.headers. Because trailer fields are attacker-controlled, an unauthenticated remote client can inject arbitrary header names and values, including X-Forwarded-For and internal authorization headers, that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application. Any http4s application using BlazeServerBuilder over HTTP/1.1 whose routes or middleware trust proxy-set headers, including X-Forwarded-For, X-Real-IP, and X-Forwarded-Host, is affected. If a fronting proxy strips or normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists, rate limits, or auditing, forge the https scheme, or inject internal authorization headers. A promoted Connection: close trailer is also honored, allowing attacker-controlled termination of pooled backend connections. This issue is fixed in versions 0.23.18 and 1.0.0-M42.
Quoted source text, attributed separately from HOL analysis.
CVSS is 7.4. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps http4s/blaze (generic), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.12 (maven), org.http4s:blaze-http_2.13 (maven) and additional mapped packages. Check affected ranges and fixed versions before updating.
| Package | Affected range | Fixed version |
|---|---|---|
| http4s/blazegeneric | < 0.23.18 || >= 1.0.0-M1, < 1.0.0-M42 | Not reported |
| org.http4s:blaze-http_2.12maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_2.12maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=1.0.0-M1 <1.0.0-M42 | 1.0.0-M42 |
| org.http4s:blaze-http_2.13maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_2.13maven | >=1.0.0-M1,<=1.0.0-M41 | 1.0.0-M42 |
| org.http4s:blaze-http_3maven | >=0 <0.23.18 | 0.23.18 |
| org.http4s:blaze-http_3maven | >=1.0.0-M1 <1.0.0-M42 | 1.0.0-M42 |
| org.http4s:blaze-http_3maven | <=0.23.17 | 0.23.18 |
| org.http4s:blaze-http_3maven | >=1.0.0-M1,<1.0.0-M42 | 1.0.0-M42 |
Published upstream
Aug 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Aug 12, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 8, 2026
blaze is a Scala library for building asynchronous pipelines, with a focus on network IO. Prior to 0.23.18 and 1.0.0-M42, blaze-server can merge HTTP/1.1 chunked-body trailer fields into Request.headers. Because trailer fields are attacker-controlled, an unauthenticated remote client can inject arbitrary header names and values, including X-Forwarded-For and internal authorization headers, that a fronting proxy sanitized from the request-header section, bypassing header-based trust decisions in the application. Any http4s application using BlazeServerBuilder over HTTP/1.1 whose routes or middleware trust proxy-set headers, including X-Forwarded-For, X-Real-IP, and X-Forwarded-Host, is affected. If a fronting proxy strips or normalizes those headers but forwards chunked bodies with trailers intact, an attacker can spoof client IP for allow-lists, rate limits, or auditing, forge the https scheme, or inject internal authorization headers. A promoted Connection: close trailer is also honored, allowing attacker-controlled termination of pooled backend connections. This issue is fixed in versions 0.23.18 and 1.0.0-M42.
Quoted source text, attributed separately from HOL analysis.