VulnerabilityPublished 11 Mar 2026Updated 12 Mar 2026

CVE-2026-31870: yhirose cpp-httplib · Uncaught Exception

Affects yhirose cpp-httplibSource CVE Database V5

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Not known to be exploited · CVSS 7.5 High : upgrade to 0.37.1 soon.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.4% chance of exploitation in 30 days – higher than 40% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 0.37.1

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 11 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade cpp-httplib and yhirose/cpp-httplib to 0.37.1.

Affected software

Product	Affected	Fixed in
yhirosecpp-httplib	Affected <0.37.1	Fixed in 0.37.1
GitHubyhirose/cpp-httplib`pkg:github/yhirose/cpp-httplib`Other threats	Affected <0.37.1	Fixed in 0.37.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

To mitigate CVE-2026-31870, organizations should upgrade all instances of cpp-httplib to version 0.37.1 or later, where the vulnerability is fixed. If upgrading immediately is not feasible, developers should implement input validation and exception handling around the parsing of the Content-Length header in their client code to catch std::invalid_argument and std::out_of_range exceptions from std::stoull. Additionally, applying network-level controls such as validating HTTP responses from trusted servers, employing TLS with certificate validation to prevent man-in-the-middle attacks, and filtering or sanitizing HTTP headers can reduce exposure. Monitoring client application logs for unexpected crashes and implementing automated restarts or failover mechanisms can help maintain availability. Finally, conducting code reviews and fuzz testing on HTTP header parsing logic in custom integrations can identify similar issues proactively.

Description

cpp-httplib is a C++11 single-file header-only cross platform HTTP/HTTPS library. Prior to 0.37.1, when a cpp-httplib client uses the streaming API (httplib::stream::Get, httplib::stream::Post, etc.), the library calls std::stoull() directly on the Content-Length header value received from the server with no input validation and no exception handling.std::stoull throws std::invalid_argument for non-numeric strings and std::out_of_range for values exceeding ULLONG_MAX. Since nothing catches these exceptions, the C++ runtime calls std::terminate(), which kills the process with SIGABRT. Any server the client connects to — including servers reached via HTTP redirects, third-party APIs, or man-in-the-middle positions can crash the client application with a single HTTP response. No authentication is required. No interaction from the end user is required. The crash is deterministic and immediate. This vulnerability is fixed in 0.37.1.

Impact

The primary impact of CVE-2026-31870 is a denial-of-service (DoS) condition caused by client application crashes. Applications using vulnerable versions of cpp-httplib for HTTP streaming can be forced to terminate unexpectedly by sending crafted HTTP responses with malicious Content-Length headers. This can disrupt service availability, degrade user experience, and potentially cause cascading failures in systems relying on these clients. Since the vulnerability can be exploited without authentication or user interaction and can be triggered by any server the client connects to, the attack surface is broad. Organizations integrating cpp-httplib in critical infrastructure, API clients, or embedded systems may face operational interruptions. While there is no direct impact on confidentiality or integrity, the availability impact is significant, especially for high-availability or real-time systems. The lack of known exploits in the wild currently limits immediate risk, but the ease of exploitation and deterministic crash behavior make this a high-risk vulnerability.

CWE-248Uncaught Exception (opens in a new tab)
Base weaknessOWASP Top 10 A10:2025: Mishandling of Exceptional Conditions (opens in a new tab)
An exception is thrown from a function, but it is not caught.
Requirements
The choice between a language which has named or unnamed exceptions needs to be done. While unnamed exceptions exacerbate the chance of not properly dealing with an exception, named exceptions suffer from the up call version of the weak base class problem.
Requirements
A language can be used which requires, at compile time, to catch all serious exceptions. However, one must make sure to use the most current version of the API as new exceptions could be added.
Implementation
Catch all relevant exceptions. This is the recommended solution. Ensure that all exceptions are handled in such a way that you can be sure of the state of your system at any given moment.
OWASP Cheat Sheets
Logging (opens in a new tab)
Error Handling (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

github.com/yhirose/cpp-httplib/security/advisories/GHSA-39q5-hh6x-jpxx (opens in a new tab)

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 18 Mar 2026, 19:04 UTC

WeaknessesCWE-248

Technical details

References

Community reviews

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