cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, when cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes the check and is then expanded to a literal \r\n byte pair inside the stored header value. This vulnerability is fixed in 0.44.0.

The remote Fedora 43 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-1d4bd0354a advisory.

    # Update to 0.48.0 (rhbz#2481109)

    ## Security fixes

    - Complete the IP-host certificate identity fix from v0.47.0 for the     Mbed TLS and wolfSSL backends. An IP-literal host is now authenticated     only via a matching iPAddress SAN, never via the certificate's Common     Name (RFC 9110)  matching what the OpenSSL backend already enforces     through X509_check_ip. Previously these backends fell back to the CN     when no IP SAN matched, and recognized IPv4 only; now IPv6 (16-byte)     iPAddress SANs are matched as well, and the CN fallback is skipped for     both IPv4 and IPv6 literal hosts (#2476)

    ## Improvements

    - Replace the strtod-based from_chars for double with a hand-written,     locale-independent parser. The only double parsed by the library is the     HTTP quality value; strtod reads the decimal separator from the global C     locale, so an embedder calling setlocale(LC_ALL, ) into a     comma-decimal locale would mis-parse q-values. The new parser always     treats . as the decimal separator and is allocation-free (Fix #2475)
    - Fix OpenSSL 4.0 deprecation warnings: fetch CA store objects via the     thread-safe X509_STORE_get1_objects() (OpenSSL 3.3+) and extract the     subject CN via X509_NAME_get_index_by_NID()/X509_NAME_get_entry()     instead of the deprecated X509_STORE_get0_objects() and     X509_NAME_get_text_by_NID(). Older OpenSSL, BoringSSL, and LibreSSL keep     using the get0 path. Verified warning-free against OpenSSL 4.0.1, 3.6.2,     and 3.0

    ## Behavior changes

    - decode_query_component() now uses strict hex parsing for     percent-escapes, consistent with decode_uri_component() and     decode_path_component(). A % followed by non-hex characters (e.g. a sign     or whitespace such as %-1, %+5, % 5) is passed through literally instead     of being accepted as a valid escape (#2472)

    Source: https://github.com/yhirose/cpp-httplib/releases/tag/v0.48.0

    # Update to 0.47.0 (rhbz#2481109, CVE-2026-46527, CVE-2026-45372, CVE-2026-45352)

    ## Security fixes

    - Fix TLS certificate chain verification bypass for IP-literal hosts on the Mbed TLS and wolfSSL backends:
    with server certificate verification enabled, SSLClient skipped chain validation entirely (any untrusted     certificate with a matching IP SAN was accepted), and WebSocketClient on Mbed TLS skipped verification     altogether. Chain verification now stays enabled for IP hosts, and certificate identity is verified post-     handshake against IP SANs on all backends. SNI is no longer sent for IP hosts on Mbed TLS and wolfSSL, per     RFC 6066 ([CVE-2026-54919](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-8ffh-4p95-g3p2))

    ## New features

    - Add Server::set_start_handler(): a callback invoked when the server is ready to accept connections,     useful when running the server in a background thread (#2467)
    - Add Client/SSLClient/WebSocketClient::enable_system_ca(bool) to opt into loading system CA certificates     alongside a custom CA. The default is unchanged: a custom CA remains exclusive. The setting carries over     to clients created for HTTPS redirects (#2471)
    - Add WebSocketClient::set_hostname_addr_map() to connect to a specific IP address while keeping the     original hostname for the handshake and certificate verification (#2463)

    ## Behavior changes

    - The request body is now read after route matching and the pre-request handler, so both the regular     handler and ContentReader paths behave the same: route matching  pre-request handler  body read     handler. A request rejected by the pre-request handler (e.g. failed per-route authentication via     req.matched_route) no longer buffers the body at all. Note: code that referenced req.body or body-derived     form fields inside the pre-request handler will now see an empty body; inspect headers, path, query     parameters, or matched_route instead
    - WebSocketClient with a custom CA no longer merges system CA certificates (it previously always merged     them). This matches SSLClient behavior; call enable_system_ca(true) to load system CA certificates     alongside the custom CA
    - Range request headers are now ignored for streaming responses of unknown length instead of producing an     invalid response (#2465)

    ## Bug fixes

    - Fix SSLClient::set_ca_cert_store() breaking custom-CA exclusivity: system CA certificates were silently     merged into the user-provided store, broadening the trust set. Also fix Client::load_ca_cert_store() not     carrying CA certificates over to clients created for HTTPS redirects
    - Fix WebSocketClient dropping the query string from the URL during the upgrade handshake, so query     parameters (e.g. auth tokens) are sent (#2468)
    - Fix a use-after-free when reconnecting a WebSocketClient after set_ca_cert_store(), and a memory leak in     the Mbed TLS and wolfSSL set_ca_cert_store() backends
    - Fix MSVC warning C4309 (truncation of constant value) in SHA padding code (#2464)
    - Cast to unsigned char before ctype calls in is_hex and is_token_char to avoid undefined behavior with     negative char values (#2469)

    Source: https://github.com/yhirose/cpp-httplib/releases/tag/v0.47.0


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Fedora 44 host has a package installed that is affected by multiple vulnerabilities as referenced in the FEDORA-2026-1b15ac058b advisory.

    # Update to 0.48.0 (rhbz#2481109)

    ## Security fixes

    - Complete the IP-host certificate identity fix from v0.47.0 for the     Mbed TLS and wolfSSL backends. An IP-literal host is now authenticated     only via a matching iPAddress SAN, never via the certificate's Common     Name (RFC 9110)  matching what the OpenSSL backend already enforces     through X509_check_ip. Previously these backends fell back to the CN     when no IP SAN matched, and recognized IPv4 only; now IPv6 (16-byte)     iPAddress SANs are matched as well, and the CN fallback is skipped for     both IPv4 and IPv6 literal hosts (#2476)

    ## Improvements

    - Replace the strtod-based from_chars for double with a hand-written,     locale-independent parser. The only double parsed by the library is the     HTTP quality value; strtod reads the decimal separator from the global C     locale, so an embedder calling setlocale(LC_ALL, ) into a     comma-decimal locale would mis-parse q-values. The new parser always     treats . as the decimal separator and is allocation-free (Fix #2475)
    - Fix OpenSSL 4.0 deprecation warnings: fetch CA store objects via the     thread-safe X509_STORE_get1_objects() (OpenSSL 3.3+) and extract the     subject CN via X509_NAME_get_index_by_NID()/X509_NAME_get_entry()     instead of the deprecated X509_STORE_get0_objects() and     X509_NAME_get_text_by_NID(). Older OpenSSL, BoringSSL, and LibreSSL keep     using the get0 path. Verified warning-free against OpenSSL 4.0.1, 3.6.2,     and 3.0

    ## Behavior changes

    - decode_query_component() now uses strict hex parsing for     percent-escapes, consistent with decode_uri_component() and     decode_path_component(). A % followed by non-hex characters (e.g. a sign     or whitespace such as %-1, %+5, % 5) is passed through literally instead     of being accepted as a valid escape (#2472)

    Source: https://github.com/yhirose/cpp-httplib/releases/tag/v0.48.0

    # Update to 0.47.0 (rhbz#2481109, CVE-2026-46527, CVE-2026-45372, CVE-2026-45352)

    ## Security fixes

    - Fix TLS certificate chain verification bypass for IP-literal hosts on the Mbed TLS and wolfSSL backends:
    with server certificate verification enabled, SSLClient skipped chain validation entirely (any untrusted     certificate with a matching IP SAN was accepted), and WebSocketClient on Mbed TLS skipped verification     altogether. Chain verification now stays enabled for IP hosts, and certificate identity is verified post-     handshake against IP SANs on all backends. SNI is no longer sent for IP hosts on Mbed TLS and wolfSSL, per     RFC 6066 ([CVE-2026-54919](https://github.com/yhirose/cpp-     httplib/security/advisories/GHSA-8ffh-4p95-g3p2))

    ## New features

    - Add Server::set_start_handler(): a callback invoked when the server is ready to accept connections,     useful when running the server in a background thread (#2467)
    - Add Client/SSLClient/WebSocketClient::enable_system_ca(bool) to opt into loading system CA certificates     alongside a custom CA. The default is unchanged: a custom CA remains exclusive. The setting carries over     to clients created for HTTPS redirects (#2471)
    - Add WebSocketClient::set_hostname_addr_map() to connect to a specific IP address while keeping the     original hostname for the handshake and certificate verification (#2463)

    ## Behavior changes

    - The request body is now read after route matching and the pre-request handler, so both the regular     handler and ContentReader paths behave the same: route matching  pre-request handler  body read     handler. A request rejected by the pre-request handler (e.g. failed per-route authentication via     req.matched_route) no longer buffers the body at all. Note: code that referenced req.body or body-derived     form fields inside the pre-request handler will now see an empty body; inspect headers, path, query     parameters, or matched_route instead
    - WebSocketClient with a custom CA no longer merges system CA certificates (it previously always merged     them). This matches SSLClient behavior; call enable_system_ca(true) to load system CA certificates     alongside the custom CA
    - Range request headers are now ignored for streaming responses of unknown length instead of producing an     invalid response (#2465)

    ## Bug fixes

    - Fix SSLClient::set_ca_cert_store() breaking custom-CA exclusivity: system CA certificates were silently     merged into the user-provided store, broadening the trust set. Also fix Client::load_ca_cert_store() not     carrying CA certificates over to clients created for HTTPS redirects
    - Fix WebSocketClient dropping the query string from the URL during the upgrade handshake, so query     parameters (e.g. auth tokens) are sent (#2468)
    - Fix a use-after-free when reconnecting a WebSocketClient after set_ca_cert_store(), and a memory leak in     the Mbed TLS and wolfSSL set_ca_cert_store() backends
    - Fix MSVC warning C4309 (truncation of constant value) in SHA padding code (#2464)
    - Cast to unsigned char before ctype calls in is_hex and is_token_char to avoid undefined behavior with     negative char values (#2469)

    Source: https://github.com/yhirose/cpp-httplib/releases/tag/v0.47.0


Tenable has extracted the preceding description block directly from the Fedora security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The remote Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS host has packages installed that are affected by a vulnerability as referenced in the USN-8470-1 advisory.

    It was discovered that cpp-httplib incorrectly percent-decoded HTTP request header values. A remote     attacker could use this to inject crafted header content possibly leading to response splitting, log     injection or proxy smuggling.

Tenable has extracted the preceding description block directly from the Ubuntu security advisory.

Note that Nessus has not tested for this issue but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.44.0, when     cpp-httplib's server parses an incoming request, it applies percent-decoding to every header value except     Location and Referer. The validity check (is_field_value) is run before decoding, so encoded %0D%0A passes     the check and is then expanded to a literal \r\n byte pair inside the stored header value. This     vulnerability is fixed in 0.44.0. (CVE-2026-45372)

Note that Nessus relies on the presence of the package as reported by the vendor.

ID	Name	Product	Family	Severity
324986	Fedora 43 : cpp-httplib (2026-1d4bd0354a)	Nessus	Fedora Local Security Checks	high
324926	Fedora 44 : cpp-httplib (2026-1b15ac058b)	Nessus	Fedora Local Security Checks	high
322948	Ubuntu 22.04 LTS / 24.04 LTS / 25.10 / 26.04 LTS : cpp-httplib vulnerability (USN-8470-1)	Nessus	Ubuntu Local Security Checks	critical
318021	Linux Distros Unpatched Vulnerability : CVE-2026-45372	Nessus	Misc.	critical

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