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NVD / CVE Program· CNA GitHub_M

CVE-2025-66570: cpp-httplib Untrusted HTTP Header Handling: Internal Header Shadowing (REMOTE*/LOCAL*)

Noroxi assessment

Priority: Monitor (action score 39/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.33% (FIRST EPSS).
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: yhirose cpp-httplib 0.27.0.

Low priority for now. Upgrade to yhirose cpp-httplib 0.27.0 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.27.0, a vulnerability allows attacker-controlled HTTP headers to influence server-visible metadata, logging, and authorization decisions. An attacker can inject headers named REMOTE_ADDR, REMOTE_PORT, LOCAL_ADDR, LOCAL_PORT that are parsed into the request header multimap via read_headers() in httplib.h (headers.emplace), then the server later appends its own internal metadata using the same header names in Server::process_request without erasing duplicates. Because Request::get_header_value returns the first entry for a header key (id == 0) and the client-supplied headers are parsed before server-inserted headers, downstream code that uses these header names may inadvertently use attacker-controlled values. Affected files/locations: cpp-httplib/httplib.h (read_headers, Server::process_request, Request::get_header_value, get_header_value_u64) and cpp-httplib/docker/main.cc (get_client_ip, nginx_access_logger, nginx_error_logger). Attack surface: attacker-controlled HTTP headers in incoming requests flow into the Request.headers multimap and into logging code that reads forwarded headers, enabling IP spoofing, log poisoning, and authorization bypass via header shadowing. This vulnerability is fixed in 0.27.0.

CriticalCVSS 9.8 · v3.1—No exploit Fix available
Published
Dec 5, 2025
Updated
Jun 17, 2026
EPSS
0.3% · 27th percentile

Report tools

JSON

Action score

39

Monitor

Low priority for now.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.3%

CISA SSVC decision

Exploitation
none
Automatable
yes
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
9.8
CNA · GitHub_M
10.0
0.2 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2025-66570

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
yhirosecpp-httplib

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • yhirose cpp-httplibbefore 0.27.0

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.

  • yhirose cpp-httplib

    • < 0.27.0affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12cpp-httplibfrom 0—
Debian:14cpp-httplibbefore 0.41.0+ds-30.41.0+ds-3
openSUSE:Leap 16.0cpp-httplibbefore 0.22.0-160000.3.10.22.0-160000.3.1
openSUSE:Tumbleweedcpp-httplibbefore 0.28.0-1.10.28.0-1.1
SUSE:Linux Enterprise Server 16.0cpp-httplibbefore 0.22.0-160000.3.10.22.0-160000.3.1

Same product

yhirose: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-45372cpp-httplib: HTTP header value percent-decoding in server-side `parse_header` enables CRLF injection
    39Monitor
  • CVE-2026-46527cpp-httplib: Malicious `X-Forwarded-For` Under Trusted-Proxy Configuration Triggers Empty `vector::front()`, Leading to Undefined Behavior and Server Crash
    34Monitor
  • CVE-2026-22776cpp-httplib vulnerable to a denial of service (DOS) using a zip bomb
    34Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2025-53628Jul 10, 2025 · cpp-httplib does not limit the length of a line
    25Monitor
  • ← EarlierCVE-2025-53629Jul 10, 2025 · cpp-httplib Unbounded Memory Allocation in Chunked/No-Length Requests Vulnerability
    30Monitor
  • Later →CVE-2025-66577Dec 5, 2025 · cpp-httplib Untrusted HTTP Header Handling: X-Forwarded-For/X-Real-IP Trust
    21Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
yhirose cpp-httplib0.27.0 · descriptionVendor (CNA)
debian:cpp-httplib0.41.0+ds-3 · Debian:14Package registry (OSV)
opensuse:cpp-httplib0.28.0-1.1 · openSUSE:TumbleweedPackage registry (OSV)
suse:cpp-httplib0.22.0-160000.3.1 · SUSE:Linux Enterprise Server 16.0Package 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.

No history yet (it accumulates with the daily EPSS job).

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 researchers

Finders, 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.

—

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.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-290 · Authentication Bypass by Spoofing

CVSS vector

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

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records