CVE-2025-8546Public exploitNetwork attack vector

Account discovery and password guessing via CAPTCHA reuse

Published Aug 5, 2025 · Updated Aug 5, 2025

CAPTCHA reuse in atjiu pybbs 6.0.0 and earlier allows remote attackers to automate repeated username and password guesses. The adminlogin, login, register, sms_code, and mobile_login handlers read the session's _captcha value but do not remove it after validation, so one solved code remains reusable. Unauthenticated access to the registration and login endpoints is sufficient to enumerate registered usernames and remove the CAPTCHA barrier from subsequent password guessing.

CVSS severity5.3
Medium
EPSS probability0.45%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

CAPTCHA reuse in atjiu pybbs 6.0.0 and earlier allows remote attackers to automate repeated username and password guesses. The adminlogin, login, register, sms_code, and mobile_login handlers read the session's _captcha value but do not remove it after validation, so one solved code remains reusable. Unauthenticated access to the registration and login endpoints is sufficient to enumerate registered usernames and remove the CAPTCHA barrier from subsequent password guessing.

The record

CVE
CVE-2025-8546
Published
Aug 5, 2025
Updated
Aug 5, 2025
Vendor
atjiu
Product
pybbs
Classifications
CWE-804, CWE-287, T1110
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 5, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 5, 2025Record 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=6.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

atjiu · pybbsversion=6.0

Published CVSS scores

5.3VulDBCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N
5.5VulDBCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N/E:P/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
5.0VulDBAV:N/AC:L/Au:N/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 exploitPublished

Weakness, pattern, technique

CWE-804Guessable CAPTCHA
CWE-287Improper Authentication
T1110Brute Force

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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