CVE-2016-3074 Detail

CVE-2016-3074

Score / Severity

9.8

Critical

EPSS

29.33%V3

Vector

Network

Published

2016-04-26
12h00 +00:00

Modified

2018-10-09
16h57 +00:00

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CVE.org

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CVE Descriptions

Integer signedness error in GD Graphics Library 2.1.1 (aka libgd or libgd2) allows remote attackers to cause a denial of service (crash) or potentially execute arbitrary code via crafted compressed gd2 data, which triggers a heap-based buffer overflow.

CVE Informations

Related Weaknesses

CWE-ID	Weakness Name	Source
CWE-681	Incorrect Conversion between Numeric Types When converting from one data type to another, such as long to integer, data can be omitted or translated in a way that produces unexpected values. If the resulting values are used in a sensitive context, then dangerous behaviors may occur.

Metrics

Metrics	Score	Severity	CVSS Vector	Source
V3.1	9.8	CRITICAL	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H More informations 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. High There is a total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server. Integrity Impact This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. High There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to 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	7.5		AV:N/AC:L/Au:N/C:P/I:P/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 : 39736

Publication date : 2016-04-25 22h00 +00:00
Author : Hans Jerry Illikainen
EDB Verified : No

Overview ======== libgd [1] is an open-source image library. It is perhaps primarily used by the PHP project. It has been bundled with the default installation of PHP since version 4.3 [2]. A signedness vulnerability (CVE-2016-3074) exist in libgd 2.1.1 which may result in a heap overflow when processing compressed gd2 data. Details ======= 4 bytes representing the chunk index size is stored in a signed integer, chunkIdx[i].size, by `gdGetInt()' during the parsing of GD2 headers: libgd-2.1.1/src/gd_gd2.c: ,---- | 53 typedef struct { | 54 int offset; | 55 int size; | 56 } | 57 t_chunk_info; `---- libgd-2.1.1/src/gd_gd2.c: ,---- | 65 static int | 66 _gd2GetHeader (gdIOCtxPtr in, int *sx, int *sy, | 67 int *cs, int *vers, int *fmt, int *ncx, int *ncy, | 68 t_chunk_info ** chunkIdx) | 69 { | ... | 73 t_chunk_info *cidx; | ... | 155 if (gd2_compressed (*fmt)) { | ... | 163 for (i = 0; i < nc; i++) { | ... | 167 if (gdGetInt (&cidx[i].size, in) != 1) { | 168 goto fail2; | 169 }; | 170 }; | 171 *chunkIdx = cidx; | 172 }; | ... | 181 } `---- `gdImageCreateFromGd2Ctx()' and `gdImageCreateFromGd2PartCtx()' then allocates memory for the compressed data based on the value of the largest chunk size: libgd-2.1.1/src/gd_gd2.c: ,---- | 371|637 if (gd2_compressed (fmt)) { | 372|638 /* Find the maximum compressed chunk size. */ | 373|639 compMax = 0; | 374|640 for (i = 0; (i < nc); i++) { | 375|641 if (chunkIdx[i].size > compMax) { | 376|642 compMax = chunkIdx[i].size; | 377|643 }; | 378|644 }; | 379|645 compMax++; | ...|... | 387|656 compBuf = gdCalloc (compMax, 1); | ...|... | 393|661 }; `---- A size of <= 0 results in `compMax' retaining its initial value during the loop, followed by it being incremented to 1. Since `compMax' is used as the nmemb for `gdCalloc()', this leads to a 1*1 byte allocation for `compBuf'. This is followed by compressed data being read to `compBuf' based on the current (potentially negative) chunk size: libgd-2.1.1/src/gd_gd2.c: ,---- | 339 BGD_DECLARE(gdImagePtr) gdImageCreateFromGd2Ctx (gdIOCtxPtr in) | 340 { | ... | 413 if (gd2_compressed (fmt)) { | 414 | 415 chunkLen = chunkMax; | 416 | 417 if (!_gd2ReadChunk (chunkIdx[chunkNum].offset, | 418 compBuf, | 419 chunkIdx[chunkNum].size, | 420 (char *) chunkBuf, &chunkLen, in)) { | 421 GD2_DBG (printf ("Error reading comproessed chunk\n")); | 422 goto fail; | 423 }; | 424 | 425 chunkPos = 0; | 426 }; | ... | 501 } `---- libgd-2.1.1/src/gd_gd2.c: ,---- | 585 BGD_DECLARE(gdImagePtr) gdImageCreateFromGd2PartCtx (gdIOCtx * in, int srcx, int srcy, int w, int h) | 586 { | ... | 713 if (!gd2_compressed (fmt)) { | ... | 731 } else { | 732 chunkNum = cx + cy * ncx; | 733 | 734 chunkLen = chunkMax; | 735 if (!_gd2ReadChunk (chunkIdx[chunkNum].offset, | 736 compBuf, | 737 chunkIdx[chunkNum].size, | 738 (char *) chunkBuf, &chunkLen, in)) { | 739 printf ("Error reading comproessed chunk\n"); | 740 goto fail2; | 741 }; | ... | 746 }; | ... | 815 } `---- The size is subsequently interpreted as a size_t by `fread()' or `memcpy()', depending on how the image is read: libgd-2.1.1/src/gd_gd2.c: ,---- | 221 static int | 222 _gd2ReadChunk (int offset, char *compBuf, int compSize, char *chunkBuf, | 223 uLongf * chunkLen, gdIOCtx * in) | 224 { | ... | 236 if (gdGetBuf (compBuf, compSize, in) != compSize) { | 237 return FALSE; | 238 }; | ... | 251 } `---- libgd-2.1.1/src/gd_io.c: ,---- | 211 int gdGetBuf(void *buf, int size, gdIOCtx *ctx) | 212 { | 213 return (ctx->getBuf)(ctx, buf, size); | 214 } `---- For file contexts: libgd-2.1.1/src/gd_io_file.c: ,---- | 52 BGD_DECLARE(gdIOCtx *) gdNewFileCtx(FILE *f) | 53 { | ... | 67 ctx->ctx.getBuf = fileGetbuf; | ... | 76 } | ... | 92 static int fileGetbuf(gdIOCtx *ctx, void *buf, int size) | 93 { | 94 fileIOCtx *fctx; | 95 fctx = (fileIOCtx *)ctx; | 96 | 97 return (fread(buf, 1, size, fctx->f)); | 98 } `---- And for dynamic contexts: libgd-2.1.1/src/gd_io_dp.c: ,---- | 74 BGD_DECLARE(gdIOCtx *) gdNewDynamicCtxEx(int initialSize, void *data, int freeOKFlag) | 75 { | ... | 95 ctx->ctx.getBuf = dynamicGetbuf; | ... | 104 } | ... | 256 static int dynamicGetbuf(gdIOCtxPtr ctx, void *buf, int len) | 257 { | ... | 280 memcpy(buf, (void *) ((char *)dp->data + dp->pos), rlen); | ... | 284 } `---- PoC === Against Ubuntu 15.10 amd64 running nginx with php5-fpm and php5-gd [3]: ,---- | $ python exploit.py --bind-port 5555 http://1.2.3.4/upload.php | [*] this may take a while | [*] offset 912 of 10000... | [+] connected to 1.2.3.4:5555 | id | uid=33(www-data) gid=33(www-data) groups=33(www-data) | | uname -a | Linux wily64 4.2.0-35-generic #40-Ubuntu SMP Tue Mar 15 22:15:45 UTC | 2016 x86_64 x86_64 x86_64 GNU/Linux | | dpkg -l|grep -E "php5-(fpm|gd)" | ii php5-fpm 5.6.11+dfsg-1ubuntu3.1 ... | ii php5-gd 5.6.11+dfsg-1ubuntu3.1 ... | | cat upload.php | <?php | imagecreatefromgd2($_FILES["file"]["tmp_name"]); | ?> `---- Solution ======== This bug has been fixed in git HEAD [4]. Full Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39736.zip Footnotes _________ [1] [http://libgd.org/] [2] [https://en.wikipedia.org/wiki/Libgd] [3] [https://github.com/dyntopia/exploits/tree/master/CVE-2016-3074] [4] [https://github.com/libgd/libgd/commit/2bb97f407c1145c850416a3bfbcc8cf124e68a19]