CVE-2019-6706 : Detail

CVE-2019-6706

7.5
/
High
Memory Corruption
1.81%V3
Network
2019-01-22
23h00 +00:00
2023-06-22
22h00 +00:00
CVE.org
NVD
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CVE Descriptions

Lua 5.3.5 has a use-after-free in lua_upvaluejoin in lapi.c. For example, a crash outcome might be achieved by an attacker who is able to trigger a debug.upvaluejoin call in which the arguments have certain relationships.

CVE Informations

Related Weaknesses

CWE-ID Weakness Name Source
CWE-416 Use After Free
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.

Metrics

Metrics Score Severity CVSS Vector Source
V3.1 7.5 HIGH CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Base: Exploitabilty Metrics

The Exploitability metrics reflect the characteristics of the thing that is vulnerable, which we refer to formally as the vulnerable component.

Attack Vector

This metric reflects the context by which vulnerability exploitation is possible.

Network

The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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

This metric describes the conditions beyond the attacker’s control that must exist in order to exploit the vulnerability.

Low

Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success when attacking the vulnerable component.

Privileges Required

This metric describes the level of privileges an attacker must possess before successfully exploiting the vulnerability.

None

The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.

User Interaction

This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable component.

None

The vulnerable system can be exploited without interaction from any user.

Base: Scope Metrics

The Scope metric captures whether a vulnerability in one vulnerable component impacts resources in components beyond its security scope.

Scope

Formally, a security authority is a mechanism (e.g., an application, an operating system, firmware, a sandbox environment) that defines and enforces access control in terms of how certain subjects/actors (e.g., human users, processes) can access certain restricted objects/resources (e.g., files, CPU, memory) in a controlled manner. All the subjects and objects under the jurisdiction of a single security authority are considered to be under one security scope. If a vulnerability in a vulnerable component can affect a component which is in a different security scope than the vulnerable component, a Scope change occurs. Intuitively, whenever the impact of a vulnerability breaches a security/trust boundary and impacts components outside the security scope in which vulnerable component resides, a Scope change occurs.

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.

Base: Impact Metrics

The Impact metrics capture the effects of a successfully exploited vulnerability on the component that suffers the worst outcome that is most directly and predictably associated with the attack. Analysts should constrain impacts to a reasonable, final outcome which they are confident an attacker is able to achieve.

Confidentiality Impact

This metric measures the impact to the confidentiality of the information resources managed by a software component due to a successfully exploited vulnerability.

None

There is no loss of confidentiality within the impacted component.

Integrity Impact

This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information.

None

There is no loss of integrity within the impacted component.

Availability Impact

This metric measures the impact to the availability of the impacted component resulting from a successfully exploited vulnerability.

High

There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Temporal Metrics

The Temporal metrics measure the current state of exploit techniques or code availability, the existence of any patches or workarounds, or the confidence in the description of a vulnerability.

Environmental Metrics

These metrics enable the analyst to customize the CVSS score depending on the importance of the affected IT asset to a user’s organization, measured in terms of Confidentiality, Integrity, and Availability.

 nvd@nist.gov
V2 5 AV:N/AC:L/Au:N/C:N/I:N/A:P nvd@nist.gov

EPSS

EPSS is a scoring model that predicts the likelihood of a vulnerability being exploited.

EPSS Score

The EPSS model produces a probability score between 0 and 1 (0 and 100%). The higher the score, the greater the probability that a vulnerability will be exploited.

EPSS Percentile

The percentile is used to rank CVE according to their EPSS score. For example, a CVE in the 95th percentile according to its EPSS score is more likely to be exploited than 95% of other CVE. Thus, the percentile is used to compare the EPSS score of a CVE with that of other CVE.
EPSS First.org

Exploit information

Exploit Database EDB-ID : 46246

Publication date : 2019-01-24 23h00 +00:00
Author : Fady Mohammed Osman
EDB Verified : No

# Exploit Title: Lua 5.3.5 # Exploit Author: Fady Mohamed Osman (https://twitter.com/fady_othman) # Exploit-db : http://www.exploit-db.com/author/?a=2986 # Blog : https://blog.fadyothman.com/ # Date: Jan. 10th 2019 # Vendor Homepage: https://www.lua.org/ # Software Link: https://www.lua.org/ftp/lua-5.3.5.tar.gz # Version: 5.3.5 # CVE ID: CVE-2019-6706 During a fuzz session using "AFL", I found a heap use after free in lua 5.3.5, after analysis of the crash I found the root cause of the vulnerability, here's the details. The function `lua_upvaluejoin` in file lapi.c at line 1287 suffers from a use after free bug when supplied the same function for parameter f1 and f2 and the same upvalue index, additionally I found that the bug is only triggered when the upvalue is closed, this happens because the `luaC_upvdeccount` function found in file lgc.c at line 678 will decrement the refcount and then free the upvalue if the refcount is zero and if the upvalue is closed. See the comments below for more explanation. -------------- LUA_API void lua_upvaluejoin (lua_State *L, int fidx1, int n1, int fidx2, int n2) { LClosure *f1; UpVal **up1 = getupvalref(L, fidx1, n1, &f1); UpVal **up2 = getupvalref(L, fidx2, n2, NULL); luaC_upvdeccount(L, *up1); //Will delete up1 *up1 = *up2; //up1 is up2 because it's the same upvalue and now it's freed. (*up1)->refcount++; //up1 is freed, yet it's used here. if (upisopen(*up1)) (*up1)->u.open.touched = 1; luaC_upvalbarrier(L, *up1); } -------------- - To trigger the bug simply use a lua program like this (this one will crash): -- f=load(function() end) interesting={} interesting[0]=string.rep("A",512) debug.upvaluejoin(f,1,f,1) --- - Another program that will not crash (unless you compile with -fsanitize=address): --- function w() local x = {} f = function() print(x) end end w() debug.upvaluejoin(f,2,f,2) --- If you want a fix you can use the patch provided here: http://lua.2524044.n2.nabble.com/CVE-2019-6706-use-after-free-in-lua-upvaluejoin-function-tc7685575.html Timeline: - Jan 10th 2019 : Vulnerability discovered and reported to lua mailing list. - Jan 23rd 2019 : CVE Identifier obtained. - Jan 25th 2019 : Fix is suggested by Matěj Cepl. Refrences: http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2019-6706 https://security-tracker.debian.org/tracker/CVE-2019-6706 https://vuldb.com/?id.130228

Products Mentioned

Configuraton 0

Lua>>Lua >> Version 5.3.5

Configuraton 0

Canonical>>Ubuntu_linux >> Version 16.04

Canonical>>Ubuntu_linux >> Version 18.04

Canonical>>Ubuntu_linux >> Version 18.10

References