How severe is CVE-2015-6835?

CVE-2015-6835 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.

Is CVE-2015-6835 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 37% (98th percentile), an estimate of the probability of exploitation in the next 30 days.

What products are affected by CVE-2015-6835?

CVE-2015-6835 primarily affects Php. In total, 63 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.

How do I fix CVE-2015-6835?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

When was CVE-2015-6835 published?

CVE-2015-6835 was published on 2016-05-16 and last updated on 2026-06-17.

CVE-2015-6835

CVE-2015-6835 is a critical-severity vulnerability in Php with a CVSS 3.x base score of 9.8. Its EPSS exploit-prediction score of 37% places it in the 98th percentile, indicating an elevated likelihood of exploitation.

Key facts

Severity: Critical (CVSS 3.x base score 9.8)
CVSS v2: 7.5
EPSS exploit prediction: 37% (98th percentile)
Actively exploited: Not listed in CISA KEV
Affected product: Php
Published: 2016-05-16
Last modified: 2026-06-17

Description

The session deserializer in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13 mishandles multiple php_var_unserialize calls, which allow remote attackers to execute arbitrary code or cause a denial of service (use-after-free) via crafted session content.

Frequently asked questions

What is CVE-2015-6835?: The session deserializer in PHP before 5.4.45, 5.5.x before 5.5.29, and 5.6.x before 5.6.13 mishandles multiple php_var_unserialize calls, which allow remote attackers to execute arbitrary code or cause a denial of service (use-after-free) via crafted session content.
How severe is CVE-2015-6835?: CVE-2015-6835 has a CVSS 3.x base score of 9.8, rated critical severity. It is exploitable over network with low attack complexity, requires no privileges and no user interaction. Impact on confidentiality is high, integrity high, and availability high.
Is CVE-2015-6835 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 37% (98th percentile), an estimate of the probability of exploitation in the next 30 days.
What products are affected by CVE-2015-6835?: CVE-2015-6835 primarily affects Php. In total, 63 product configurations (CPEs) are listed as vulnerable; see the affected-products list for the exact versions.
How do I fix CVE-2015-6835?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
When was CVE-2015-6835 published?: CVE-2015-6835 was published on 2016-05-16 and last updated on 2026-06-17.

References

Affected products (63)

cpe:2.3:a:php:php:5.6.0:alpha1:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:alpha2:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:alpha3:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:alpha4:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:alpha5:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:beta1:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:beta2:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:beta3:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.0:beta4:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.1:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.2:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.3:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.4:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.5:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.6:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.7:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.8:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.9:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.10:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.11:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.6.12:*:*:*:*:*:*:*
cpe:2.3:a:php:php:*:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha1:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha2:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha3:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha4:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha5:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:alpha6:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:beta1:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:beta2:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:beta3:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:beta4:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:rc1:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.0:rc2:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.1:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.2:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.3:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.4:*:*:*:*:*:*:*
cpe:2.3:a:php:php:5.5.5:*:*:*:*:*:*:*

More vulnerabilities in Php

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CVE-2008-5557 — Critical (CVSS 10.0): Heap-based buffer overflow in ext/mbstring/libmbfl/filters/mbfilter_htmlent.c in the mbstring extension in PHP 4.3.0…

All CVEs affecting Php →

Threat intelligence

Threat-intel indicators referencing this CVE:

45.84.120.3 (ipv4-addr)
221.161.235.168 (ipv4-addr)
200.196.50.91 (ipv4-addr)
187.141.71.166 (ipv4-addr)
187.110.238.50 (ipv4-addr)
113.164.66.10 (ipv4-addr)
103.38.219.22 (ipv4-addr)
103.20.122.54 (ipv4-addr)