CVE-2016-15015Network attack vector

Webhook signature disclosure via non-constant-time comparison

Published Jan 8, 2023 · Updated Aug 6, 2024

Timing side channel in viafintech Barzahlen PHP SDK 2.0.0 allows remote attackers to infer a valid webhook HMAC through repeated probes. Webhook::verify compares the supplied HTTP_BZ_SIGNATURE header with the calculated HMAC using PHP's non-constant-time equality operator, allowing response time to reveal matching prefixes. Repeated network access to a merchant's webhook endpoint is required; successful recovery supports forged callbacks, while no direct service interruption is documented.

CVSS severity2.6
Low
EPSS probability0.63%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Timing side channel in viafintech Barzahlen PHP SDK 2.0.0 allows remote attackers to infer a valid webhook HMAC through repeated probes. Webhook::verify compares the supplied HTTP_BZ_SIGNATURE header with the calculated HMAC using PHP's non-constant-time equality operator, allowing response time to reveal matching prefixes. Repeated network access to a merchant's webhook endpoint is required; successful recovery supports forged callbacks, while no direct service interruption is documented.

The record

CVE
CVE-2016-15015
Published
Jan 8, 2023
Updated
Aug 6, 2024
Vendor
viafintech
Product
Barzahlen PHP SDK
Classifications
CWE-208, CWE-203
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 8, 2023CVE publishedPublication date reported by the CVE source.
  2. Aug 6, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=2.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

viafintech · Barzahlen PHP SDKversion=2.0

Published CVSS scores

5.3NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
2.6VulDBCVSS:3.1/AV:A/AC:H/PR:L/UI:N/S:U/C:L/I:N/A:N
1.4VulDBAV:A/AC:H/Au:S/C:P/I:N/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-208Observable Timing Discrepancy
CWE-203Observable Discrepancy

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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