VulnerabilityPublished 16 Dec 2025

CVE-2025-68113: altcha-lib · Misinterpretation of Input

Affects altcha-libSource CVE Database V5

Not known to be exploited · CVSS 6.5 Medium : upgrade to 1.4.1 when convenient.

Data as of 26 Oct 2026, 10:12 UTC

CVSS 3.1 base score

6.5Medium

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

EPSS: 0.4% chance of exploitation in 30 days – higher than 39% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.4.1, 1.3.1, 1.3.0 +1

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

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

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: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 16 Dec 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 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.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, 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 to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
npmaltcha-lib`pkg:npm/altcha-lib`Other threats	Affected <1.4.1	Fixed in 1.4.1
Packagistaltcha-org/altcha`pkg:composer/altcha-org/altcha`Other threats	Affected <1.3.1	Fixed in 1.3.1
Mavenorg.altcha/altcha`pkg:maven/org.altcha/altcha`Other threats	Affected <1.3.0	Fixed in 1.3.0
Goaltcha-org/altcha`pkg:golang/altcha-org/altcha`Other threats	Affected <1.0.0	Fixed in 1.0.0
RubyGemsaltcha`pkg:gem/altcha`Other threats	Affected <1.0.0	Fixed in 1.0.0
PyPIaltcha`pkg:pypi/altcha`Other threats	Affected <1.0.0	Fixed in 1.0.0

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

AI-suggested

European organizations using altcha-lib or its language-specific packages should immediately upgrade to the patched versions: altcha Golang package 1.0.0, Rubygem 1.0.0, pip 1.0.0, Erlang 1.0.0, npm 1.4.1, Composer 1.3.1, and Maven 1.3.0 or later. Until upgrades are applied, implement the recommended mitigation by appending a delimiter (e.g., "?expires=<time>&") to the salt value before HMAC computation to enforce unambiguous parameter binding and prevent payload splicing. Review server-side replay detection and handling mechanisms to ensure they effectively reject reused challenges beyond expiration. Conduct thorough testing to verify that bot mitigation controls are functioning as intended post-mitigation. Additionally, monitor logs for unusual patterns indicative of replay attacks or automated abuse. Incorporate this vulnerability into risk assessments and incident response plans. Finally, maintain awareness of altcha-org security advisories for any further updates or exploit reports.

Description

ALTCHA is privacy-first software for captcha and bot protection. A cryptographic semantic binding flaw in ALTCHA libraries allows challenge payload splicing, which may enable replay attacks. The HMAC signature does not unambiguously bind challenge parameters to the nonce, allowing an attacker to reinterpret a valid proof-of-work submission with a modified expiration value. This may allow previously solved challenges to be reused beyond their intended lifetime, depending on server-side replay handling and deployment assumptions. The vulnerability primarily impacts abuse-prevention mechanisms such as rate limiting and bot mitigation. It does not directly affect data confidentiality or integrity. This issue has been addressed by enforcing explicit semantic separation between challenge parameters and the nonce during HMAC computation. Users are advised to upgrade to patched versions, which include version 1.0.0 of the altcha Golang package, version 1.0.0 of the altcha Rubygem, version 1.0.0 of the altcha pip package, version 1.0.0 of the altcha Erlang package, version 1.4.1 of the altcha-lib npm package, version 1.3.1 of the altcha-org/altcha Composer package, and version 1.3.0 of the org.altcha:altcha Maven package. As a mitigation, implementations may append a delimiter to the end of the `salt` value prior to HMAC computation (for example, `<salt>?expires=<time>&`). This prevents ambiguity between parameters and the nonce and is backward-compatible with existing implementations, as the delimiter is treated as a standard URL parameter separator.

Impact

For European organizations, this vulnerability poses a risk primarily to the effectiveness of bot mitigation and abuse-prevention systems that rely on altcha-lib or its language-specific implementations. Attackers exploiting this flaw can replay previously solved captcha challenges beyond their expiration, potentially enabling automated abuse such as credential stuffing, scraping, or denial-of-service attempts that bypass rate limiting. This can lead to increased fraudulent transactions, account takeover attempts, or service degradation. While the vulnerability does not directly expose sensitive data or allow unauthorized data modification, the circumvention of bot defenses can indirectly facilitate broader attacks. Organizations in sectors with high online interaction—such as e-commerce, banking, telecommunications, and government services—are particularly at risk. Additionally, services relying on altcha-lib for privacy-first captcha solutions may face reputational damage if abuse escalates. The impact depends on the deployment specifics and server-side replay protections in place, but the potential for undermining automated abuse controls is significant.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 23 Dec 2025, 04:48 UTC

WeaknessesCWE-115, CWE-347

Technical details

References

Community reviews

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