CVE-2024-13939
Fractal String\ \
Raw vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:NCVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.
Summary
CVE-2024-13939 is a high-severity Observable Timing Discrepancy (CWE-208) vulnerability in Fractal String\. Its CVSS base score is 7.5 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Steganography (T1001.002); ranked at the 29th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog.
The strongest mitigations our analysis identified map to IA-6 (Authentication Feedback) and SA-11 (Developer Testing and Evaluation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2024-13939 is a timing side-channel vulnerability in the String::Compare::ConstantTime Perl module through version 0.321. The flaw arises because the equals function returns false immediately if the input string and secret string have different lengths, enabling attackers to infer the secret string's length through observable timing differences without revealing its contents. This issue is classified under CWE-208 (Observable Timing Discrepancy) and CWE-203 (Observable Discrepancy), with a CVSS v3.1 base score of 7.5 (AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N).
Any remote, unauthenticated attacker can exploit this vulnerability over the network with low complexity and no user interaction. By repeatedly submitting strings of varying lengths for comparison against a secret string—such as in authentication tokens, passwords, or cryptographic keys—the attacker measures response times to determine the exact length of the secret, potentially aiding further attacks like brute-forcing or enumeration.
The vulnerability is documented in the module's source code at https://metacpan.org/release/FRACTAL/String-Compare-ConstantTime-0.321/view/lib/String/Compare/ConstantTime.pm#TIMING-SIDE-CHANNEL, which explicitly notes: "If the lengths of the strings are different, because equals returns false right away the size of the secret string may be leaked (but not its contents)." This is similar to CVE-2020-36829, and practitioners should upgrade to newer versions of the module if available or avoid using it for constant-time comparisons of secrets.
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2025-8542
Vulnerability Data
String::Compare::ConstantTime for Perl through 0.321 is vulnerable to timing attacks that allow an attacker to guess the length of a secret string. As stated in the documentation: "If the lengths of the strings are different, because equals returns false right…
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away the size of the secret string may be leaked (but not its contents)." This is similar to CVE-2020-36829
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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- 1 hardening rule · 1 OS baseline
V11.2.4
Mitigating Controls (NIST 800-53 r5) AI
Obscures authentication feedback so that success/failure differences are not observable to attackers.
Developer testing can include timing analysis or side-channel test cases that reveal observable timing discrepancies.
Requires error messages to avoid revealing exploitable details, directly stopping observable response discrepancies.
Engineering principles can mandate constant-time algorithms and side-channel resistance so timing discrepancies are never introduced.
Requiring approved cryptographic modules and algorithms implicitly demands implementations free of observable timing leaks.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
Secure SDLC practices directly require constant-time implementations that eliminate observable timing discrepancies.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.